Methods and apparatus related to low latency within a data center

ABSTRACT

In one embodiment, an apparatus includes a switch core that has a multi-stage switch fabric. The multi-stage switch fabric has a set of ingress ports and a set of egress ports. The switch core can be configured to be coupled to a set of edge devices via the set of ingress ports and the set of egress ports. The switch core can be configured to receive a packet from an ingress port from the set of ingress ports. The switch core can be configured to send a set of cells associated with the packet from the ingress port to an egress port from the set of egress ports without a store-and-forward delay associated with a zero-load latency for the switch core.

CROSS-REFERENCE OF RELATED PATENT APPLICATIONS

This patent application claims priority to and the benefit of U.S.Patent Application No. 61/098,516 entitled “Systems, Apparatus andMethods for a Data Center” and filed on Sep. 19, 2008; and claimspriority to and the benefit of U.S. Patent Application No. 61/096,209entitled “Methods and Apparatus Related to Flow Control within a DataCenter” and filed on Sep. 11, 2008; each of which is incorporated hereinby reference in its entirety.

This patent application is a continuation-in-part of U.S. patentapplication Ser. No. 12/343,728 entitled “Methods and Apparatus forTransmission of Groups of Cells via a Switch Fabric” and filed on Dec.24, 2008; a continuation-in-part of U.S. patent application Ser. No.12/345,500 entitled “System Architecture for a Scalable and DistributedMulti-Stage Switch Fabric” and filed on Dec. 29, 2008; acontinuation-in-part of U.S. patent application Ser. No. 12/345,502entitled “Methods and Apparatus Related to a Modular SwitchArchitecture” and filed on Dec. 29, 2008; a continuation-in-part of U.S.patent application Ser. No. 12/242,224 entitled “Methods and Apparatusfor Flow Control Associated with Multi-Staged Queues” and filed on Sep.30, 2008, which claims priority to and the benefit of U.S. PatentApplication No. 61/096,209 entitled “Methods and Apparatus Related toFlow Control within a Data Center” and filed on Sep. 11, 2008; and acontinuation-in-part of U.S. patent application Ser. No. 12/242,230entitled “Methods and Apparatus for Flow-Controllable Multi-StagedQueues” and filed on Sep. 30, 2008, which claims priority to and thebenefit of U.S. Patent Application No. 61/096,209 entitled “Methods andApparatus Related to Flow Control within a Data Center” and filed onSep. 11, 2008. Each of the above-identified applications is incorporatedherein by reference in its entirety.

This patent application is related to U.S. patent application Ser. No.12/495,337 entitled “Methods and Apparatus Related to Any-to-AnyConnectivity within a Data Center” and filed on Jun. 30, 2009; U.S.patent application Ser. No. 12/495,344 entitled “Methods and ApparatusRelated to Lossless Operation within a Data Center” and filed on Jun.30, 2009; U.S. patent application Ser. No. 12/495,361 entitled “Methodsand Apparatus Related to Flow Control within a Data Center SwitchFabric” and filed on Jun. 30, 2009; and U.S. patent application Ser. No.12/495,364 entitled “Methods and Apparatus Related to Virtualization ofData Center Resources” and filed on Jun. 30, 2009; each of which isincorporated herein by reference in its entirety.

SUMMARY

In one embodiment, an apparatus includes a switch core that has amulti-stage switch fabric. The multi-stage switch fabric has a set ofingress ports and a set of egress ports. The switch core can beconfigured to be coupled to a set of edge devices via the set of ingressports and the set of egress ports. The switch core can be configured toreceive a packet from an ingress port from the set of ingress ports. Theswitch core can be configured to send a set of cells associated with thepacket from the ingress port to an egress port from the set of egressports without a store-and-forward delay associated with a zero-loadlatency for the switch core.

BACKGROUND

Embodiments relate generally to data center equipment, and moreparticularly to architectures, apparatus and methods for data centersystems having a switch core and edge devices.

Known architectures for data center systems involve overly involved andcomplex approaches that increase the costs and latency of such systems.For example, some known data center networks consist of three or morelayers of switches where Ethernet and/or Internet Protocol (IP) packetprocessing is performed at each layer. Packet processing and queuingoverhead unnecessarily repeated at each layer directly increases thecosts and end-to-end latency. Similarly, such known data center networksdo not typically scale in a cost effective manner: an increase in thenumber servers for a given data center systems often requires theaddition of ports, and thus the addition of more devices, at each layerof the data center systems. Such poor scalability increases the cost ofsuch data center systems.

Thus, a need exists for improved data center systems including improvedarchitectures, apparatus and methods.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a system block diagram of a data center (DC), according to anembodiment.

FIG. 2 is a schematic diagram that illustrates an example of a portionof a data center having any-to-any connectivity, according to anembodiment.

FIG. 3 is a schematic diagram that illustrates logical groups ofresources associated with a data center, according to an embodiment.

FIG. 4 is a schematic diagram that illustrates a switch fabric that canbe included in a switch core, according to an embodiment.

FIG. 5 is a schematic diagram that illustrates a switch fabric system,according to an embodiment.

FIG. 6 is a schematic diagram that illustrates a portion of the switchfabric system of FIG. 5, according to an embodiment.

FIG. 7 is a schematic diagram that illustrates a portion of the switchfabric system of FIG. 5, according to an embodiment.

FIGS. 8 and 9 show front and back perspective views respectively, of ahousing used to house a switch fabric, according to an embodiment.

FIG. 10 shows a portion of the housing of FIG. 8, according to anembodiment.

FIGS. 11 and 12 are schematic diagrams that illustrate a switch fabricin a first configuration and a second configuration respectively,according to another embodiment.

FIG. 13 is a schematic diagram that illustrates flow of data associatedwith a switch fabric, according to an embodiment.

FIG. 14 is a schematic diagram that illustrates flow control within theswitch fabric shown in FIG. 13, according to an embodiment

FIG. 15 is a schematic diagram that illustrates a buffer module,according to an embodiment.

FIG. 16A is a schematic block diagram of an ingress schedule module andan egress schedule module configured to coordinate transmissions ofgroups of cells via a switch fabric of a switch core, according to anembodiment.

FIG. 16B is a signaling flow diagram that illustrates signaling relatedto the transmission of the group of cells, according to an embodiment.

FIG. 17 is a schematic block diagram that illustrates two groups ofcells queued at an ingress queue disposed on an ingress side of a switchfabric, according to an embodiment.

FIG. 18 is a schematic block diagram that illustrates two groups ofcells queued at an ingress queue disposed on an ingress side of a switchfabric, according to another embodiment.

FIG. 19 is a flowchart that illustrates a method for schedulingtransmission of a group of cells via a switch fabric, according to anembodiment.

FIG. 20 is a signaling flow diagram that illustrates processing ofrequest sequence values associated with transmission requests, accordingto an embodiment.

FIG. 21 is a signaling flow diagram that illustrates response sequencevalues associated with transmission responses, according to anembodiment.

FIG. 22 is a schematic block diagram that illustrates multiple stages offlow-controllable queues, according to an embodiment.

FIG. 23 is a schematic block diagram that illustrates multiple stages offlow-controllable queues, according to an embodiment.

FIG. 24 is a schematic block diagram that illustrates a destinationcontrol module configured to define a flow control signal associatedwith multiple receive queues, according to an embodiment.

FIG. 25 is a schematic diagram that illustrates a flow control packet,according to an embodiment.

DETAILED DESCRIPTION

FIG. 1 is a schematic diagram that illustrates a data center (DC) 100(e.g., a super data center, an idealized data center), according to anembodiment. The data center 100 includes a switch core (SC) 180 operablyconnected to four types of peripheral processing devices 170: computenodes 110, service nodes 120, routers 130, and storage nodes 140. Inthis embodiment, a data center management (DCM) module 190 is configuredto control (e.g., manage) operation of the data center 100. In someembodiments, the data center 100 can be referred to as a data center. Insome embodiments, the peripheral processing devices can include one ormore virtual resources such as virtual machines.

Each of the peripheral processing devices 170 is configured tocommunicate via the switch core 180 of the data center 100.Specifically, the switch core 180 of the data center 100 is configuredto provide any-to-any connectivity between the peripheral processingdevices 170 at relatively low latency. For example, switch core 180 canbe configured to transmit (e.g., convey) data between one or more of thecompute nodes 110 and one or more of the storage nodes 140. In someembodiments, the switch core 180 can have at least hundreds or thousandsof ports (e.g., egress ports and/or ingress ports) through whichperipheral processing devices 170 can transmit and/or receive data. Theperipheral processing devices 170 can include one or more networkinterface devices (e.g., a network interface card (NIC), a 10 Gigabit(Gb) Ethernet Converged Network Adapter (CNA) device) through which theperipheral processing device 170 can send signals to and/or receivesignals from the switch core 180. The signals can be sent to and/orreceived from the switch core 180 via a physical link and/or a wirelesslink operably coupled to the peripheral processing devices 170. In someembodiments, the peripheral processing devices 170 can be configured tosend to and/or receive signals from the switch core 180 based on one ormore protocols (e.g., an Ethernet protocol, a multi-protocol labelswitching (MPLS) protocol, a fibre channel protocol, afibre-channel-over Ethernet protocol, an Infiniband-related protocol).

In some embodiments, the switch core 180 can be (e.g., can function as)a single consolidated switch (e.g., a single large-scale consolidatedL2/L3 switch). In other words, the switch core 180 can be configured tooperate as a single logical entity (e.g., a single logical networkelement). The switch core 180 can be configured to connect (e.g.,facilitate communication between) the compute nodes 110, the storagenodes 140, the services nodes 120, and/or the routers 130 within thedata center 100. In some embodiments, the switch core 180 can beconfigured to communicate via interface devices configured to transmitdata at a rate of at least 10 Gb/s. In some embodiments, the switch core180 can be configured to communicate via interface devices (e.g.,fibre-channel interface devices) configured to transmit data at a rateof, for example, 2 Gb/s, 4, Gb/s, 8 Gb/s, 10 Gb/s, 40 Gb/s, 100 Gb/sand/or faster link speeds.

Although the switch core 180 can be logically centralized, theimplementation of the switch core 180 can be highly distributed, forexample, for reliability. For example, portions of the switch core 180can be physically distributed across, for example, many chassis. In someembodiments, for example, a processing stage of the switch core 180 canbe included in a first chassis and another processing stage of theswitch core 180 can be included in a second chassis. Both of theprocessing stages can logically function as part of a singleconsolidated switch. More details related to architecture of the switchcore 180 are described in connection with FIGS. 4 through 13.

As shown in FIG. 1, the switch core 180 includes an edge portion 185 anda switch fabric 187. The edge portion 185 can include edge devices (notshown) that can function as gateway devices between the switch fabric187 and the peripheral processing devices 170. In some embodiments, theedge devices can be referred to as access switches or as a networkdevices.

Data can be processed at the peripheral processing devices 170, at theswitch core 180, the switch fabric 187 of the switch core 180, and/or atthe edge portion 185 of the switch core 180 (e.g., at edge devicesincluded in the edge portion 185) based on different platforms. Forexample, communication between one or more of the peripheral processingdevices 170 and an edge device at the edge portion 185 can be a streamof data packets defined based on an Ethernet protocol or a non-Ethernetprotocol. The data packets can be parsed into cells at the edge deviceof edge portion 185, and the cells can be transmitted from the edgedevice to the switch fabric 187. The cells can be parsed into segmentsand transmitted within the switch fabric 187 as segments (also can bereferred to as flits in some embodiments). In some embodiments, the datapackets can be parsed into cells at a portion of the switch fabric 187.More details related to processing of data packets, cells, and/orsegments within components of the data center are described below.

In some embodiments, edge devices within the edge portion 185 can beconfigured to classify, for example, data packets received at the switchcore 180 from the peripheral processing devices 170. The switch core 180can be defined so that classification of data packets is not performedin the switch fabric 187. Accordingly, although the switch fabric 187can have multiple stages, the stages are not topological hops where datapacket classification is performed. More details related to packetclassification within a data center are described in connection withFIG. 5 and FIG. 19. Additional details related to packet classificationassociated within a data center are described in U.S. patent applicationSer. No. 12/242,168 entitled “Methods and Apparatus Related to PacketClassification Associated with a Multi-Stage Switch,” filed Sep. 30,2008, and U.S. patent application Ser. No. 12/242,172, entitled “Methodsand Apparatus for Packet Classification Based on Policy Vectors,” filedSep. 30, 2008, both of which are incorporated herein by reference intheir entireties.

In some embodiments, one or more portions of the data center 100 can be(or can include) a hardware-based module (e.g., an application-specificintegrated circuit (ASIC), a digital signal processor (DSP), a fieldprogrammable gate array (FPGA)) and/or a software-based module (e.g., amodule of computer code, a set of processor-readable instructions thatcan be executed at a processor). In some embodiments, one or more of thefunctions associated with the data center 100 can be included indifferent modules and/or combined into one or more modules. For example,the data center management module 190 can be a combination of hardwaremodules and software modules configured to manage the resources (e.g.,resources of the switch core 180) within the data center 100.

One or more of the compute nodes 110 can be a general-purposecomputational engine that can include, for example, processors, memory,and/or one or more network interface devices (e.g., a network interfacecard (NIC)). In some embodiments, the processors within a compute nodes110 can be part of one or more cache coherent domains.

In some embodiments, the compute nodes 110 can be host devices, servers,and/or so forth. In some embodiments, one or more of the compute nodes110 can have virtualized resources such that any compute node 110 (or aportion thereof) can be substituted for any other compute node 110 (or aportion thereof) within the data center 100.

One or more of the storage nodes 140 can be devices that include, forexample, processors, memory, locally-attached disk storage, and/or oneor more network interface devices. In some embodiments, the storagenodes 140 can have specialized modules (e.g., hardware modules and/orsoftware modules) configured to enable, for example, one or more of thecompute nodes 110 to read data from and/or write data to one or more ofthe storage nodes 140 via the switch core 180. In some embodiments, oneor more of the storage nodes 140 can have virtualized resources so thatany storage node 140 (or a portion thereof) can be substituted for anyother storage node 140 (or a portion thereof) within the data center100.

One or more of the services nodes 120 can be an open systemsinterconnection (OSI) layer-4 through layer-7 device that can include,for example, processors (e.g., network processors), memory, and/or oneor more network interface devices (e.g., 10 Gb Ethernet devices). Insome embodiments, the services nodes 120 can include hardware and/orsoftware configured to perform computations on relatively heavy networkworkloads. In some embodiments, the services nodes 120 can be configuredperform computations on a per packet basis in a relatively efficientfashion (e.g., more efficiently than can be performed at, for example, acompute node 110). The computations can include, for example, statefulfirewall computations, intrusion detection and prevention (IDP)computations, extensible markup language (XML) accelerationcomputations, transmission control protocol (TCP) terminationcomputations, and/or application-level load-balancing computations. Insome embodiments, one or more of the services nodes 120 can havevirtualized resources so that any service node 120 (or a portionthereof) can be substituted for any other service node 120 (or a portionthereof) within the data center 100.

One or more of the routers 130 can be networking devices configured toconnect at least a portion of the data center 100 to another network(e.g., the global Internet). For example, as shown in FIG. 1, the switchcore 180 can be configured to communicate through the routers 130 tonetwork 135 and network 137. Although not shown, in some embodiments,one or more of the routers 130 can enable communication betweencomponents (e.g., peripheral processing devices 170, portions of theswitch core 180) within the data center 100. The communication can bedefined based on, for example, a layer-3 routing protocol. In someembodiments, one or more of the routers 130 can have one or more networkinterface devices (e.g., 10 Gb Ethernet devices) through which therouters 130 can send signals to and/or receive signals from, forexample, the switch core 180 and/or other peripheral processing devices170.

More details related to virtualized resources within a data center areset forth in co-pending U.S. patent application Ser. No. 12/346,623,filed Dec. 30, 2008, entitled , “Method and Apparatus for Determining aNetwork Topology During Network Provisioning,” co-pending U.S. patentapplication Ser. No. 12/346,632, filed Dec. 30, 2008, entitled, “Methodsand Apparatus for Distributed Dynamic Network Provisioning,” andco-pending U.S. patent application Ser. No. 12/346,630, filed Dec. 30,2008, entitled , “Methods and Apparatus for Distributed Dynamic NetworkProvisioning,” all of which are hereby incorporated by reference hereinin their entireties.

As discussed above, the switch core 180 can be configured to function asa single universal switch connecting any peripheral processing device170 in the data center 100 to any other peripheral processing device170. Specifically, the switch core 180 can be configured to providedany-to-any connectivity between the peripheral processing devices 170(e.g., a relatively large number of peripheral processing devices 170)with the switch core 180 having substantially no perceptible limitsexcept those imposed by the bandwidth of the network interfaces devicesconnecting the peripheral processing devices 170 to the switch core 180and by speed-of-light signaling delays (also referred to asspeed-of-light latency). Said differently, the switch core 180 can beconfigured so that each peripheral processing device 170 appears to beinterconnected directly to every other peripheral processing devicewithin the data center 100. In some embodiments, the switch core 180 canbe configured so that the peripheral processing devices 170 cancommunicate at line rate (or at substantially line rate) via the switchcore 180. A schematic representation of any-to-any connectivity is shownin FIG. 2.

FIG. 2 is a schematic diagram that illustrates an example of a portionof a data center having any-to-any connectivity, according to anembodiment. As shown in FIG. 2, a peripheral processing device PD (froma group of peripheral processing devices 210) is connected to each ofthe peripheral processing devices 210 via switch core 280. In thisembodiment, only connections from peripheral processing device PD to theother peripheral processing devices 210 (excluding peripheral processingdevice PD) are shown for clarity.

In some embodiments, the switch core 280 can be defined so that theswitch core 280 is fair in the sense that the bandwidth of a destinationlink between the peripheral processing devices PD and the otherperipheral processing devices 210 is shared substantially equitablyamong contending peripheral processing devices 210. For example, whenseveral (or all) of the peripheral processing devices 210 shown in FIG.2 are attempting to access peripheral processing device PD at a giventime, the bandwidth (e.g., instantaneous bandwidth) available to each ofthe peripheral processing devices 280 to access the peripheralprocessing device PD will be substantially equal. In some embodiments,the switch core 280 can be configured so that several (or all) of theperipheral processing devices 210 can communicate with the peripheralprocessing device PD at full bandwidth (e.g., full bandwidth of theperipheral processing device PD) and/or in a non-blocking fashion.Moreover, the switch core 280 can be configured so that access to theperipheral processing device PD by a peripheral processing device (fromthe peripheral processing devices 210) may not be limited by other links(e.g., existing or attempted) between other peripheral processingdevices and the peripheral processing device PD.

In some embodiments, any-to-any connectivity, low latency, fairness,and/or so forth, which are attributes of the switch core 280, can enableperipheral processing devices 210 of a given type (e.g., of a storagenode type, of a compute node type) connected to (e.g., in communicationwith) the switch core 280 to be treated interchangeably (e.g.,independent of location relative to other processing devices 210 and theswitch core 280). This can be referred to as fungibility, and canfacilitate the efficiency and simplicity of a data center includingswitch core 280. The switch core 280 can have the attributes ofany-to-any connectivity and/or fairness even though the switch core 280may have a large number of ports (e.g., more than 1000 ports) such thateach port operates at a relatively high speed (e.g., operate a speedgreater than 10 Gb/s). This can be achieved without specializedinterconnects included in, for example, a supercomputer and/or withoutperfect a-priori knowledge of all communication patterns. More detailsrelated to the architecture of the switch core having any-to-anyconnectivity and/or fairness are described, at least in part, inconnection with FIGS. 4 through 13.

Referring back to FIG. 1, in some embodiments, the data center 100 canbe configured to allow for flexible oversubscription. In someembodiments, through flexible oversubscription, the relative cost ofnetwork infrastructure (e.g., network infrastructure related to theswitch core 180) can be reduced compared with the cost of, for example,computing and storage. For example, resources (e.g., all resources)within the switch core 180 of the data center 100 can operate asflexible pooled resources so that underutilized resources that areassociated with a first application (or set of applications) can bedynamically provisioned for use by a second application (or set ofapplications) during, for example, peak processing by the secondapplication. Accordingly, the resources (or a subset of the resources)of the data center 100 can be configured to handle oversubscription moreefficiently than if resources were strictly allocated as a silo ofresources to a particular application (or set of applications). Ifmanaged as silos of resources, oversubscription can be implemented onlywithin the silo of resources rather than across, for example, the entiredata center 100. In some embodiments, one or more of the protocolsand/or components within the data center 100 can be based on openstandards (e.g., Institute of Electrical and Electronics Engineers(IEEE) standards, Internet Engineering Task Force (IETF) standards,International Committee for Information Technology Standards (INCITS)standards).

In some embodiments, the data center 100 can support security modelsthat permit a wide range of policies to be implemented. For example, thedata center 100 can support no communication policies, whereapplications reside in separate virtual data centers of the data center100 but can share the same physical peripheral processing devices (e.g.,compute nodes 100, storage nodes 140) and network infrastructure (e.g.,switch core 180). In some configurations, the data center 100 cansupport multiple processes that are part of the same application andneed to communicate with almost no limitations. In some configurations,the data center 100 can also support policies that may require, forexample, deep packet inspection, stateful firewalls, and/or statelessfilters.

The data center 100 can have an end-to-end application to applicationlatency (also can be referred to as end-to-end latency) defined based onsource latency, zero-load latency, congestion latency, and destinationlatency. In some embodiments, source latency can be, for example, timeexpended during processing at a source peripheral processing device(e.g., time expended by software and/or a NIC). Similarly, destinationlatency can be, for example, time expended during processing at adestination peripheral processing device (e.g., time expended bysoftware and/or a NIC). In some embodiments, zero-load latency can bethe speed-of-light delay plus the processing and store-and-forwarddelays inside, for example, the switch core 180. In some embodiments,congestion latency can be, for example, queuing delays caused by backupsin the network. The data center 100 can have a low end-to-end latencythat enables desirable application performance for applications that aresensitive to latency such as applications with real-time constraintsand/or applications with high levels of inter-process communicationrequirements.

The zero-load latency of the switch core 180 can be significantly lessthan that of a data center core portion having an interconnection ofEthernet-based hops. In some embodiments, for example, the switch core180 can have a zero-load latency (excluding speed-of-light latency) froman ingress port of the switch core 180 to an egress port of the switchcore 180 of less than 6 microseconds. In some embodiments, for example,the switch core 180 can have a zero-load latency (excluding congestionlatency and speed-of-light latency) of less than 12 microseconds.Ethernet-based data center core portions may have significantly higherlatencies because of, for example, undesirable levels of congestion(e.g., congestion between links). The congestion within theEthernet-based data center core portions can be exacerbated by theinability of the Ethernet-based data center core (or management devicesassociated with the Ethernet-based data center core) to handle thecongestion in a desirable fashion. In addition, latencies within anEthernet-based data center core portion can be non-uniform because thecore portion can have different numbers of hops between differentsource-destination pairs and/or many store-and-forward switch nodeswhere classification of data packets is performed. In contrast,classification of the switch core 180 is performed at the edge portion185 and is not performed in the switch fabric 187, and the switch core180 has a deterministic cell-based switch fabric 187. For example, thelatency of processing of cells through the switch fabric 187 (but notthe paths the cells through the switch fabric 187) can be predictable.

The switch core 180 of the data center 100 can providelossless-end-to-end packet delivery, at least in part, based on flowcontrol schemes implemented within the data center 100. For example,scheduling of transmission of data (e.g., data associated with datapackets) via the switch fabric 187 is performed on a cell basis using arequest-grant scheme (also can be referred to as a request-authorizationscheme). Specifically, cells are transmitted into the switch fabric 187(e.g., transmitted into the switch fabric 187 from the edge portion 185)after a request to transmit the cells has been granted based onsubstantially guaranteed delivery (without loss). Once admitted into theswitch fabric 187, the cells are processed within the switch fabric 187as segments. Flow of the segments within the switch fabric 187 canfurther be controlled, for example, so that the segments are not lostwhen congestion within the switch fabric 187 is detected. More detailsrelated to processing of cells and segments within the switch core 180are described below.

Also, flow of data packets in the switch core 180, which can be parsedinto cells and segments, can be controlled at the peripheral processingdevices 170 based on a fine grain flow control scheme. In someembodiments, fine grain flow control can be implemented based on stagesof queues. This type of fine grain flow control can prevent (orsubstantially prevent) head-of-line blocking, which can result in poornetwork utilization. The fine grain flow control can also be used toreduce (or minimize) latency within the switch core 180. In someembodiments, fine grain flow control can enable high-performance blockoriented disk traffic to and from the peripheral processing devices 170,which may not be achieved using Ethernet and Internet Protocol (IP)networks in a desirable fashion. More details related to fine grain flowcontrol are described in connection with FIGS. 22 through 25.

In some embodiments, the data center 100, and, in particular, the switchcore 180 can have a modular architecture. Specifically, the switch core180 of the data canter 100 can be implemented initially at small scaleand can be expanded (e.g., incrementally expanded) as needed. The switchcore 180 can be expanded substantially without disruption to continuousoperation of the existing network and/or can be expanded withoutconstraints on where the new equipment of the switch core 180 should bephysically located.

In some embodiments, one or more portions of the switch core 180 can beconfigured to operate based on virtual private networks (VPN's).Specifically, the switch core 180 can be partitioned so that one or moreof the peripheral processing devices 170 can be configured tocommunicate via overlapping or non-overlapping virtual partitions of theswitch core 180. The switch core 180 can also be parsed into virtualizedresources that have disjoint or overlapping subsets. In other words, theswitch core 180 can be a single switch that can be partitioned in aflexible fashion. In some embodiments, this approach can enablenetworking at scale once within the consolidated switch core 180 of thedata center 100. This can be contrasted with data centers that can be acollection of separate scalable networks that may each have customizedand/or specialized resources. In some embodiments, networking resourcesthat define the switch core 180 can be pooled so that they can be usedefficiently.

In some embodiments, the data center management module 190 can beconfigured to define multiple levels of virtualization of the physical(and/or virtual) resources that define the data center 100. For example,the data center management module 190 can be configured to definemultiple levels of virtualization that can represent the breadth ofapplications of the data center 100. In some embodiments, a lower level(of two levels) can include a virtual application cluster (VAC), whichcan be a set of physical (or virtual) resources assigned to a singleapplication belonging to (e.g., controlled by) one or more entities(e.g., an administrative entity, a financial institution). An upperlevel (of two levels) can include a virtual data center (VDC), which caninclude a set of VAC's belonging to (e.g., controlled by) one or moreentities. In some embodiments, the data center 100 can include a numberof VAC's that can each belong to a different administrative entity.

FIG. 3 is a schematic diagram that illustrates logical groups 300 ofresources associated with a data center, according to an embodiment. Asshown in FIG. 3, the logical groups 300 include virtual data centerVDC₁, virtual data center VDC₂, and virtual data center VDC₃(collectively referred to as VDCs). Also, as shown in FIG. 3, each ofthe VDCs includes virtual application clusters VACs (e.g., VAC₃₂ withinVDC₃). Each VDC represents logical groups of physical or virtualportions of a data center (e.g., portions of a switch core, portions ofperipheral processing devices and/or a virtual machine within aperipheral processing device) such as data center 100 shown in FIG. 1.Each VAC within the VDCs represents logical groups of, for example,peripheral processing devices such as compute nodes. For example, VDC₁can represent a logical group of a portion of a physical data center,and VAC₂₂ can represent a logical group of peripheral processing devices370 within VDC₁. As shown in FIG. 3, each VDC can be managed based on aset of policies PYs (also can be referred to as business rules) that canbe configured to, for example, define the permitted range of operatingparameters for applications running within the VDCs. In someembodiments, the VDCs can be referred to as a first tier of logicalresources, and the VACs can be referred to as a second tier of logicalresources.

In some embodiments, VDCs (and VACs) can be established so thatresources associated with a data center can be managed in a desirablefashion by, for example, entities that use (e.g., lease, own,communicate through) the resources of the data center and/oradministrators of the resources of the data center. For example, VDC₁can be a virtual data center associated with a financial institution,and VDC₂ can be a virtual data center associated with telecommunicationsservice provider. Accordingly, the policy PY₁ can be defined by thefinancial institution so that VDC₁ (and the physical and/or virtual datacenter resources associated with VDC₁) can be managed in a manner thatis different from (or similar to) a manner in which VDC₂ (and thephysical and/or virtual data center resources associated with VDC₂) ismanaged based on policy PY₂, which can be defined by thetelecommunications service provider. In some embodiments, one or morepolicies (e.g., a portion of policy PY₁) can be established by a networkadministrator that, when implemented, provide information securityand/or firewalls between VDC₁, which is associated with the financialinstitution, and VDC₂, which is associated with the telecommunicationsservice provider.

In some embodiments, policies can be associated with (e.g., integratedwithin) a data center management (not shown). For example, VDC₂ can bemanaged based on policy PY₂ (or a subset of policy PY₂). In someembodiments, the data center management can be configured to, forexample, monitor the real-time performance of applications within theVDCs and/or can be configured to allocate or de-allocate resourcesautomatically to satisfy the respective policies for applications withinthe VDCs. In some embodiments, policies can be configured to operatebased on time thresholds. For example, one or more policies can beconfigured to function based on periodic events (e.g., predictableperiodic events) such as variations in a parameter value (e.g., atraffic level) at a specified time of day or during a day of week.

In some embodiments, policies can be defined based on a high levellanguage. Accordingly, the policies can be specified in a relativelyaccessible fashion. Examples of policies include information securingpolicies, failure isolation policies, firewall policies, performanceguarantees policies (e.g., policies related to service levels to beimplemented by an application), and/or other administrative policies(e.g., management isolation policies) related to protection or archivingof information.

In some embodiments, the policies can be implemented at a packetclassification module that can be configured to, for example, classify adata packet (e.g., an IP packet, a session control protocol packet, amedia packet, a data packet defined at a peripheral processing device).For example, the policies can be implemented within a packetclassification module of an access switch within an edge portion of aswitch core. Classifying can include any processing performed so thatthe data packet can be processed within a data center (e.g., a switchcore of a data center) based on a policy. In some embodiments, thepolicy can include one or more policy conditions that are associatedwith an instruction that can be executed. The policy can be, forexample, a policy to route a data packet to a particular destination(instruction) if the data packet has a specified type of network address(policy condition). Packet classification can include determiningwhether or not the policy condition has been satisfied so that theinstruction can be executed. For example, one or more portions (e.g., afield, a payload, an address portion, a port portion) of the data packetcan be analyzed by the packet classification module based on a policycondition defined within a policy. When the policy condition issatisfied, the data packet can be processed based on an instructionassociated with the policy condition.

In some embodiments, one or more portions of the logical groups 300 canbe configured to be operate in a “lights out” manner from multipleremote locations—such as a separate location for each of the VDCs andone or two master locations to control the logical groups 300. In someembodiments, a data center with logical groups such as those shown inFIG. 3 can be configured to function without personnel physically at thedata center site. In some embodiments, a data center can have sufficientredundant resources to accommodate the occurrence of failures such asfailure of one or more of the peripheral processing devices (e.g., aperipheral processing device within a VAC), failure of the data centermanagement module, and/or failure of a component of a switch core. Whenmonitoring software within a data center (e.g., within data centermanagement of the data center) indicates that failures have reached apredefined threshold, personnel can be notified and/or dispatched toreplace the failed components.

As shown in FIG. 3, the VDCs can be mutually exclusive logical groups.In some embodiments, resources (e.g., virtual resources, physicalresources) of a data center (such as that shown in FIG. 1) can bedivided into different logical groups 300 (e.g., different tiers oflogical groups) than those shown in FIG. 3. In some embodiments, two ormore of the VDCs of the logical groups 300 can be overlapping. Forexample, a first VDC can share resources (e.g., physical resources,virtual resources) of a data center with a second VDC. Specifically, aportion of a switch core of the first VDC can be shared with the secondVDC. In some embodiments, for example, resources included in a VAC ofthe first VDC can be included in a VAC of the second VDC.

In some embodiments, one or more of the VDCs can be manually defined(e.g., manually defined by a network administrator) and/or automaticallydefined (e.g., automatically defined based on a policy). In someembodiments, the VDCs can be configured to change (e.g., changedynamically). For example, a VDC (e.g., VDC₁) can include a specifiedset of resources during a period of time and can include a different setof resources (e.g., mutually exclusive set of resources, overlapping setof resources) during a different period of time (e.g., mutuallyexclusive period of time, overlapping period of time).

In some embodiments, one or more portions of a data center can bedynamically provisioned in response to, before, or during a changerelated to a VDC (e.g., a migration of a portion of the VDC such as avirtual machine of the VDC). For example, a switch core of a data centercan include multiple network devices such as network switches, eachstoring a library of configuration templates including provisioninginstructions for services provided by and/or required by virtualmachines. When a virtual machine migrates to and/or is instantiated orstarted on a server connected to a port of a network switch of theswitch core, the server can send to the network switch an identifierrelated to a service provided by the virtual machine. The network devicecan select a configuration template from the library of configurationtemplates based on the identifier, and provision the port and/or theserver based on the configuration template. Thus, the task ofprovisioning network ports and/or devices can be distributed (e.g.,distributed in an automated fashion, distributed without redefiningtemplates) across network switches in the switch core, and can varydynamically as virtual machines or resources are migrated amongperipheral processing devices.

In some embodiments, provisioning can include various types or forms ofdevice and/or software module setup, configuration, and/or adjustment.For example, provisioning can include configuring a network devicewithin a data center such as a network switch based on a policy such asone of the policies PY shown in FIG. 3. More specifically, for example,provisioning related to a data center can include one or more of thefollowing: configuring a network device to operate as a network routeror a network switch; alter routing tables of a network device; updatesecurity policies and/or device addresses or identifiers of devicesoperatively coupled to a network device; selecting which networkprotocols a network device will implement; setting network segmentidentifiers such as virtual local area network (“VLAN”) tags for a portof a network device; and/or applying access control lists (“ACLs”) to anetwork device. A portion of a data center can be provisioned orconfigured such that rules and/or access restrictions defined by thepolicy (e.g., policy PY₃) are applied (e.g., applied through aclassification process) to data packets that pass through the portion ofthe data center.

In some embodiments, virtual resources associated with a data center canbe provisioned. A virtual resource can be, for example, a softwaremodule implementing a virtual switch, virtual router, or virtual gatewaythat is configured to operate as an intermediary between a physicalnetwork and virtual resources hosted by a host device such as a server.In some embodiments, a virtual resource can be hosted by the hostdevice. In some embodiments, provisioning can include establishing avirtual port or connection between a virtual resource and a virtualdevice.

More details related to virtualized resources within a data center areset forth in co-pending U.S. patent application Ser. No. 12/346,623,filed Dec. 30, 2008, entitled , “Method and Apparatus for Determining aNetwork Topology During Network Provisioning,” co-pending U.S. patentapplication Ser. No. 12/346,632, filed Dec. 30, 2008, entitled ,“Methods and Apparatus for Distributed Dynamic Network Provisioning,”and co-pending U.S. patent application Ser. No. 12/346,630, filed Dec.30, 2008, entitled, “Methods and Apparatus for Distributed DynamicNetwork Provisioning,” all of which have been incorporated by referenceherein in their entireties.

FIG. 4 is a schematic diagram that illustrates a switch fabric 400 thatcan be included in a switch core, according to an embodiment. In someembodiments, the switch fabric 400 can be included in switch core suchas switch core 180 shown in FIG. 1. As shown in FIG. 4, switch fabric400 is a three-stage, non-blocking Clos network and includes a firststage 440, a second stage 442, and a third stage 444. The first stage440 includes modules 412. Each module 412 of the first stage 440 is anassembly of electronic components and circuitry. In some embodiments,for example, each module is an application-specific integrated circuit(ASIC). In other embodiments, multiple modules are contained on a singleASIC. In some embodiments, each module is an assembly of discreteelectrical components. In some embodiments, a switch fabric withmultiple stages can be referred to as a multi-stage switch fabric.

In some embodiments, each module 412 of the first stage 440 can be acell switch. The cell switches can be configured to effectively redirectdata (e.g., segments) as it flows through the switch fabric 400. In someembodiments, for example, each cell switch can include multiple inputports operatively coupled to write interfaces on a memory buffer (e.g.,a cut-through buffer). In some embodiments, the memory buffer can beincluded in a buffer module. Similarly, a set of output ports can beoperatively coupled to read interfaces on the memory buffer. In someembodiments, the memory buffer can be a shared memory buffer implementedusing on-chip static random access memory (SRAM) to provide sufficientbandwidth for all input ports to write one incoming cell (e.g., aportion of a data packet) per time period and all output ports to readone outgoing cell per time period. Each cell switch operates similar toa crossbar switch that can be reconfigured subsequent each time period.More details related to a shared memory buffer are described inconnection with FIG. 15, and in co-pending U.S. patent application Ser.No. 12/415,517, filed on Mar. 31, 2009, entitled, “Methods and ApparatusRelated to a Shared Memory Buffer for Variable-Sized Cells,” which isincorporated herein by reference in its entirety.

In alternate embodiments, each module of the first stage can be acrossbar switch having input bars and output bars. Multiple switcheswithin the crossbar switch connect each input bar with each output bar.When a switch within the crossbar switch is in an “on” position, theinput is operatively coupled to the output and data can flow.Alternatively, when a switch within the crossbar switch is in an “off”position, the input is not operatively coupled to the output and datacannot flow. Thus, the switches within the crossbar switch control whichinput bars are operatively coupled to which output bars.

Each module 412 of the first stage 440 includes a set of input ports 460configured to receive data as it enters the switch fabric 400. In thisembodiment, each module 412 of the first stage 440 includes the samenumber of input ports 460.

Similar to the first stage 440, the second stage 442 of the switchfabric 400 includes modules 414. The modules 414 of the second stage 442are structurally similar to the modules 412 of the first stage 440. Eachmodule 414 of the second stage 442 is operatively coupled to each moduleof the first stage 440 by a data path 420. Each data path 420 betweeneach module of the first stage 440 and each module 414 of the secondstage 442 is configured to facilitate data transfer from the modules 412of the first stage 440 to the modules 414 of the second stage 442.

The data paths 420 between the modules 412 of the first stage 440 andthe modules 414 of the second stage 442 can be constructed in any mannerconfigured to facilitate data transfer from the modules 412 of the firststage 440 to the modules 414 of the second stage 442 in a desirablefashion (e.g., in an effective fashion). In some embodiments, forexample, the data paths are optical connectors between the modules. Inother embodiments, the data paths are within a midplane. Such a midplanecan be similar to that described in further detail herein. Such amidplane can be effectively used to connect each module of the secondstage with each module of the first stage. In still other embodiments,the modules are contained within a single chip package and the datapaths are electrical traces.

In some embodiments, the switch fabric 400 is a non-blocking Closnetwork. Thus, the number of modules 414 of the second stage 442 of theswitch fabric 400 varies based on the number of input ports 460 of eachmodule 412 of the first stage 440. In a rearrangeably non-blocking Closnetwork (e.g., a Benes network), the number of modules 414 of the secondstage 442 is greater than or equal to the number of input ports 460 ofeach module 412 of the first stage 440. Thus, if n is the number ofinput ports 460 of each module 412 of the first stage 440 and m is thenumber of modules 414 of the second stage 442, m≧n. In some embodiments,for example, each module of the first stage has five input ports. Thus,the second stage has at least five modules. All five modules of thefirst stage are operatively coupled to all five modules of the secondstage by data paths. Said another way, each module of the first stagecan send data to any module of the second stage.

The third stage 444 of the switch fabric 400 includes modules 416. Themodules 416 of the third stage 444 are structurally similar to themodules 412 of the first stage 440. The number of modules 416 of thethird stage 444 is equivalent to the number of modules 412 of the firststage 440. Each module 416 of the third stage 444 includes output ports462 configured to allow data to exit the switch fabric 400. Each module416 of the third stage 444 includes the same number of output ports 462.Further, the number of output ports 462 of each module 416 of the thirdstage 444 is equivalent to the number of input ports 460 of each module412 of the first stage 440.

Each module 416 of the third stage 444 is connected to each module 414of the second stage 442 by a data path 424. The data paths 424 betweenthe modules 414 of the second stage 442 and the modules 416 of the thirdstage 444 are configured to facilitate data transfer from the modules414 of the second stage 442 to the modules 416 of the third stage 444.

The data paths 424 between the modules 414 of the second stage 442 andthe modules 416 of the third stage 444 can be constructed in any mannerconfigured to effectively facilitate data transfer from the modules 414of the second stage 442 to the modules 416 of the third stage 444. Insome embodiments, for example, the data paths are optical connectorsbetween the modules. In other embodiments, the data paths are within amidplane. Such a midplane can be similar to that described in furtherdetail herein. Such a midplane can be effectively used to connect eachmodule of the second stage with each module of the third stage. In stillother embodiments, the modules are contained within a single chippackage and the data paths are electrical traces.

FIG. 5 is a schematic diagram that illustrates a switch fabric system500, according to an embodiment. Switch fabric system 500 includesmultiple input/output modules 502, a first set of cables 540, a secondset of cables 542, and a switch fabric 575. The switch fabric 575includes a first switch fabric portion 571 disposed within a housing 570or chassis, and a second switch fabric portion 573 disposed within ahousing 572 or chassis.

The input/output modules 502 are configured to send data to and/orreceive data from the first switch fabric portion 571 and/or the secondswitch fabric portion 573. Additionally, each input/output module 502can include a parsing function, a classifying function, a forwardingfunction, and/or a queuing and scheduling function. Thus, packetparsing, packet classifying, packet forwarding, and packet queuing andscheduling all occur prior to a data packet entering the first switchfabric portion 571 and/or the second switch fabric portion 573.Accordingly, these functions do not need to be preformed at each stageof the switch fabric 575, and each module of the switch fabric portions571, 573 (described in further detail herein) do not need to includecapabilities to perform these functions. This can reduce the cost, powerconsumption, cooling requirements and/or physical area required for eachmodule of the switch fabric portions 571, 573. This also reduces thelatency associated with the switch fabric. In some embodiments, forexample, the end-to-end latency (i.e., time it takes to send datathrough the switch fabric from an input/output module to anotherinput/output module) can be lower than the end-to-end latency of aswitch fabric system using an Ethernet protocol. In some embodiments,the throughput of the switch fabric portions 571, 573 is constrainedonly by the connection density of the switch fabric system 500 and notby power and/or thermal limitations. In some embodiments, theinput/output modules 502 (and/or the functionality associated with theinput/output modules 502) can be included in, for example, an edgedevice within a edge portion of a switch core such as that shown inFIG. 1. The parsing function, classifying function, forwarding function,and queuing and scheduling function can be preformed similar to thefunctions disclosed in U.S. patent application Ser. No. 12/242,168entitled “Methods and Apparatus Related to Packet ClassificationAssociated with a Multi-Stage Switch,” filed Sep. 30, 2008, and U.S.patent application Ser. No. 12/242,172, entitled “Methods and Apparatusfor Packet Classification Based on Policy Vectors,” filed Sep. 30, 2008,both of which have been incorporated herein by reference in theirentireties.

Each input/output module 502 is configured to connect to a first end ofa cable of the first set of cables 540 and a first end of a cable of thesecond set of cables 542. Each cable 540 is disposed between aninput/output module 502 and the first switch fabric portion 571.Similarly, each cable 542 is disposed between an input/output module 502and the second switch fabric portion 573. Using the first set of cables540 and the second set of cables 542, each input/output module 502 cansend data to and/or receive data from the first switch fabric portion571 and/or the second switch fabric portion 573, respectively.

The first set of cables 540 and the second set of cables 542 can beconstructed of any material suitable to transfer data between theinput/output modules 502 and the switch fabric portions 571, 573. Insome embodiments, for example, each cable 540, 542 is constructed ofmultiple optical fibers. In such an embodiment, each cable 540, 542 canhave twelve transmit and twelve receive fibers. The twelve transmitfibers of each cable 540, 542 can include eight fibers for transmittingdata, one fiber for transmitting a control signal, and three fibers forexpanding the data capacity and/or for redundancy. Similarly, the twelvereceive fibers of each cable 540, 542 have eight fibers for transmittingdata, one fiber for transmitting a control signal, and three fibers forexpanding the data capacity and/or for redundancy. In other embodiments,any number of fibers can be contained within each cable.

A first switch fabric portion 571 is used in conjunction with a secondswitch fabric portion 573 for redundancy and/or greater capacity. Inother embodiments, only one switch fabric portion is used. In stillother embodiments, more than two switch fabric portions are used forincreased redundancy and/or greater capacity. For example, four switchfabric portions can be operatively coupled to each input/output moduleby, for example, four cables. The second switch fabric portion 573 isstructurally and functionally similar to the first switch fabric 571.Accordingly, only the first switch fabric portion 571 is described indetail herein.

FIG. 6 shows a portion of the switch fabric system 500 of FIG. 5,including the first switch fabric portion 571, in greater detail. Thefirst switch fabric portion 571 includes interface cards 510, which areassociated with a first stage and a third stage of the first switchfabric portion 571; interface cards 516, which are associated with asecond stage of the first switch fabric portion 571; and a midplane 550.In some embodiments, the first switch fabric portion 571 includes eightinterface cards 510, which are associated with the first stage and thethird stage of the first switch fabric, and eight interface cards 516,which are associated with the second stage of the first switch fabric.In other embodiments, a different number of interface cards associatedwith the first stage and the third stage of the first switch fabricand/or a different number of interface cards associated with the secondstage of the first switch fabric can be used.

As shown in FIG. 6, each input/output module 502 is operatively coupledto an interface card 510 via one of the cables of the first set ofcables 540. In some embodiments, for example, each of eight interfacecards 510 is operatively coupled to sixteen input/output modules 502, asdescribed in further detail herein. Thus, the first switch fabricportion 571 can be coupled to 128 input/output modules (16×8=128). Eachof the 128 input/output modules 502 can send data to and receive datafrom the first switch fabric portion 571.

Each interface card 510 is connected to each interface card 516 via themidplane 550. Thus, each interface card 510 can send data to and receivedata from each interface card 516, as described in further detailherein. Using a midplane 550 to connect the interface cards 510 to theinterface cards 516, decreases the number of cables used to connect thestages of the first switch fabric portion 571.

FIG. 7 shows a first interface card 510′, the midplane 550, and a firstinterface card 516′, in greater detail. Interface card 510′ isassociated with the first stage and the third stage of the first switchfabric portion 571, and interface card 516′ is associated with thesecond stage of the first switch fabric portion 571. Each interface card510 is structurally and functionally similar to the first interface card510′. Likewise, each interface card 516 is structurally and functionallysimilar to the first interface card 516′.

The first interface card 510′ includes multiple cable connector ports560, a first module system 512, a second module system 514, and multiplemidplane connector ports 562. For example, FIG. 7 shows the firstinterface card 510′ having sixteen cable connector ports 560 and eightmidplane connector ports 562. Each cable connector port 560 of the firstinterface card 510′ is configured to receive a second end of a cablefrom the first set of cables 540. Thus, as stated above, sixteen cableconnector ports 560 on each of the eight interface cards 510 are used toreceive the 128 cables (16×8=128). While shown in FIG. 7 as havingsixteen cable connector ports 560, in other embodiments, any number ofcable connector ports can be used, such that each cable from the firstset of cables can be received by a cable connector port in the firstswitch fabric. For example, if sixteen interface cards are used, eachinterface card can include eight cable connector ports.

The first module system 512 and the second module system 514 of thefirst interface card 510′ each includes a module of the first stage ofthe first switch fabric portion 571 and a module of the third stage ofthe first switch fabric portion 571. In some embodiments, eight cableconnector ports of the sixteen cable connector ports 560 are operativelycoupled to the first module system 512 and the remaining eight cableconnector ports of the sixteen cable connector ports 560 are operativelycoupled to the second module system 514. Both the first module system512 and the second module system 514 are operatively coupled to each ofthe eight midplane connector ports 562 of interface card 510′.

The first module system 512 and the second module system 514 of firstinterface card 510′ are ASICs. The first module system 512 and thesecond module system 514 are instances of the same ASIC. Thus,manufacturing costs can be decreased because multiple instances of asingle ASIC can be produced. Further, a module of the first stage of thefirst switch fabric portion 571 and a module of the third stage of thefirst switch fabric are both included on each ASIC.

In some embodiments, each midplane connector port of the eight midplaneconnector ports 562 has twice the data capacity of each cable connectorport of the sixteen cable connector ports 560. Thus, instead of havingeight data transmit and eight data receive connections, the eightmidplane connector ports 562 each has sixteen data transmit and sixteendata receive connections. Thus, the bandwidth of the eight midplaneconnector ports 562 is equivalent to the bandwidth of the sixteen cableconnector ports 560. In other embodiments, each midplane connector porthas thirty-two data transmit and thirty-two data receive connections. Insuch an embodiment, each cable connector port has sixteen data transmitand sixteen data receive connections.

The eight midplane connector ports 562 of the first interface card 510′are connected to the midplane 550. The midplane 550 is configured toconnect each interface card 510 which is associated with the first stageand the third stage of the first switch fabric portion 571, to eachinterface card 516 which is associated with the second stage of thefirst switch fabric portion 571. Thus, the midplane 550 ensures thateach midplane connector port 562 of each interface card 510 is connectedto a midplane connector port 580 of a different interface card 516. Saidanother way, no two midplane connector ports of the same interface card510 are operatively coupled to the same interface card 516. Thus, themidplane 550 allows each interface card 510 to send data to and receivedata from any of the eight interface cards 516.

While FIG. 7 shows a schematic view of the first interface card 510′ themidplane 550, and the first interface card 516′, in some embodiments,the interface cards 510, the midplane 550, and the interface cards 516are physically positioned similar to the horizontally positionedinterface cards 620, the midplane 640, and vertically positionedinterface cards 630, respectively, shown in FIGS. 5 through 7 anddescribed in further detail herein. Thus, the modules associated withthe first stage and the modules associated with the third stage (both onthe interface cards 510) are placed on one side of the midplane 550, andthe modules associated with the second stage (on the interface cards516) are placed on the opposite side of the midplane 550. This topologyallows each module associated with the first stage to be operativelycoupled to each module associated with the second stage, and each moduleassociated with the second stage to be operatively coupled to eachmodule associated with the third stage.

The first interface card 516′ includes multiple midplane connector ports580, a first module system 518, and a second module system 519. Themultiple midplane connector ports 580 are configured to send data to andreceive data from any of the interface cards 510, via the midplane 550.In some embodiments, the first interface card 516′ includes eightmidplane connector ports 580.

The first module system 518 and the second module system 519 of thefirst interface card 516′ are operatively coupled to each midplaneconnector port 580 of the first interface card 516′. Thus, through themidplane 550, each of the module systems 512, 514 associated with thefirst stage and the third stage of the first switch fabric portion 571is operatively coupled to each of the module systems 518, 519 associatedwith the second stage of the first switch fabric portion 571. Saidanother way, each module system 512, 514 associated with the first stageand the third stage of the first switch fabric portion 571 can send datato and receive data from any of the module systems 518, 519 associatedwith the second stage of the first switch fabric portion 571, and viceversa. Specifically, a module associated with the first stage within amodule system 512 or 514 can send data to a module associated with thesecond stage within a module system 518 or 519. Similarly, the moduleassociated with the second stage within the module system 518 or 519 cansend data to a module associated with the third stage within a modulesystem 512 or 514. In other embodiments, the module associated with thethird stage can send data and/or control signals to the moduleassociated with the second stage, and the module associated with thesecond stage can send data and/or control signals to the moduleassociated with the first stage.

In embodiments where each module of the first stage of the first switchfabric portion 571 has eight inputs (i.e., two modules per eachinterface card 510), the second stage of the first switch fabric portion571 can have at least eight modules for the first switch fabric portion571 to remain rearrangeably non-blocking. Thus, the second stage of thefirst switch fabric portion 571 has at least eight modules and isrearrangeably non-blocking. In some embodiments, twice the number ofmodules of the second stage are used to facilitate expansion of theswitch fabric system 500 from a three-stage switch fabric to afive-stage switch fabric, as described in further detail herein. In sucha five-stage switch fabric, the second stage supports twice theswitching throughput as the second stage within the three-stage switchfabric of the switch fabric system 500. For example, in someembodiments, sixteen modules of the second stage can be used tofacilitate future expansion of the switch fabric system 500 from athree-stage switch fabric to a five-stage switch fabric.

The first module system 518 and the second module system 519 of firstinterface card 516′ are ASICs. The first module system 518 and thesecond module system 519 are instances of the same ASIC. Additionally,in some embodiments, the first module system 518 and the second modulesystem 519 which are associated with the second stage of the firstswitch fabric portion 571, are instances of the ASIC also used for thefirst module system 512 and the second module system 514 of the firstinterface card 510′, which are associated with the first stage and thethird stage of the first switch fabric portion 571. Thus, manufacturingcosts can be decreased because multiple instances of a single ASIC canbe used for each of the module systems in the first switch fabricportion 571.

In use, data is transferred from a first input/output module 502 to asecond input/output module 502 via the first switch fabric portion 571.The first input/output module 502 sends data into the first switchfabric portion 571 via a cable of the first set of cables 540. The datapasses through a cable connector port 560 of one of the interface cards510′ and into the first stage module within a module system 512 or 514.

The first stage module within the module system 512 or 514 forwards thedata to a second stage module within a module system 518 or 519, bysending the data through one of the midplane connector ports 562 of theinterface card 510′, through the midplane 550, and to one of theinterface cards 516′. The data enters the interface card 516′ through amidplane connector port 580 of the interface card 516′. The data is thensent to the second stage module within a module system 518 or 519.

The second stage module, determines how the second input/output module502 is connected and redirects the data back to the interface card 510′,via the midplane 550. Because each module system 518 or 519 isoperatively coupled to each module system 512 and 514 on interface card510′, the second stage module within the module system 518 or 519 candetermine which third stage module within the module system 512 or 514is operatively coupled to the second input/output module and send thedata accordingly.

The data is sent to the third stage module within a module system 512,514 on the interface card 510′. The third stage module then sends thedata to the second input/output module of the input/output modules 502via a cable of the first set of cables 540 through a cable connectorport 560.

In other embodiments, instead of the first stage module sending the datato a single second stage module, the first stage module separates thedata into separate portions (e.g., cells) and forwards a portion of thedata to each second stage module to which the first stage module isoperatively coupled (e.g., in this embodiment, every second stage modulereceives a portion of the data). Each second stage module thendetermines how the second input/output module is connected and redirectsthe portions of the data back to a single third stage module. The thirdstage module then reconstructs the received portions of the data andsends the data to the second input/output module.

FIGS. 8-10 show a housing 600 (i.e., a chassis) used to house a switchfabric (such as first switch fabric portion 571 described above),according to an embodiment. The housing 600 includes a casing 610, amidplane 640, horizontally positioned interface cards 620 and verticallypositioned interface cards 630. FIG. 8 shows a front view of the casing610 in which eight horizontally positioned interface cards 620 can beseen disposed within the casing 610. FIG. 9 shows a rear view of thecasing 610 in which eight vertically positioned interface cards 630 canbe seen disposed within the casing 610.

Each horizontally positioned interface card 620 is operatively coupledto each vertically positioned interface card 630 by the midplane 640(see FIG. 10). The midplane 640 includes a front surface 642, a rearsurface 644 and an array of receptacles 650 that connect the frontsurface 642 with the rear surface 644, as described below. As shown inFIG. 10, the horizontally positioned interface cards 620 includemultiple midplane connector ports 622 that connect to the receptacles650 on the front surface 642 of the midplane 640. Similarly, thevertically positioned interface cards 630 include multiple midplaneconnector ports 632 that connect to the receptacles on the rear surface644 of the midplane 640. In this manner, a plane defined by eachhorizontally positioned interface card 620 intersects a plane defined byeach vertically positioned interface card 630.

The receptacles 650 of the midplane 640 operatively couple eachhorizontally-positioned interface card 620 to each vertically-positionedinterface card 630. The receptacles 650 facilitate the transfer ofsignals between a horizontally-positioned interface card 620 and avertically-positioned interface card 630. In some embodiments, forexample, the receptacles 650 can be multiple-pin connectors configuredto receive multiple pin-connectors disposed on the midplane connectorports 622, 632 of the interface cards 620, 630, hollow tubes that allowa horizontally-positioned interface card 620 to directly connect with avertically-positioned interface card 630, and/or any other deviceconfigured to operatively couple two interface cards. Using such amidplane 640, each horizontally-positioned interface card 620 isoperatively coupled to each vertically-positioned interface card 630without routing connections (e.g., electrical traces) on the midplane.

FIG. 10 shows a midplane including a total of 64 receptacles 650positioned in an 8×8 array. In such an embodiment, eighthorizontally-positioned interface cards 620 can be operatively coupledto eight vertically-positioned interface cards 630. In otherembodiments, any number of receptacles can be included on the midplaneand/or any number of horizontally-positioned interface cards can beoperatively coupled to any number of vertically-positioned interfacecards through the midplane.

If the first switch fabric portion 571 were housed in housing 600, forexample, each interface card 510 associated with the first stage and thethird stage of the first switch fabric portion 571 would be positionedhorizontally and each interface card 516 associated with the secondstage of the first switch fabric portion 571 would be positionedvertically. Thus, each interface card 510 associated with the firststage and the third stage of the first switch fabric portion 571 iseasily connected to each interface card 516 associated with the secondstage of the first switch fabric portion 571, through the midplane 640.In other embodiments, each interface card associated with the firststage and the third stage of the first switch fabric portion ispositioned vertically and each interface card associated with the secondstage of the first switch fabric portion is positioned horizontally. Instill other embodiments, each interface card associated with the firststage and the third stage of the first switch fabric portion can bepositioned at any angle with respect to the housing and each interfacecard associated with the second stage of the first switch fabric portioncan be positioned at an angle orthogonal to the angle of the interfacecard associated with the first stage and the third stage of the firstswitch fabric portion with respect to the housing.

FIGS. 11 and 12 are schematic diagrams that illustrate a switch fabric1100 in a first configuration and a second configuration, respectively,according to an embodiment. The switch fabric 1100 includes multipleswitch fabric systems 1108.

Each switch fabric system 1108 includes multiple input/output modules1102, a first set of cables 1140, a second set of cables 1142, a firstswitch fabric portion 1171 disposed within a housing 1170, and a secondswitch fabric portion 1173 disposed within a housing 1172. Each switchfabric system 1108 is structurally and functionally similar. Further,the input/output modules 1102, the first set of cables 1140, and thesecond set of cables 1142 are structurally and functionally similar tothe input/output modules 202, the first set of cables 240, and thesecond set of cables 242, respectively.

When the switch fabric 1100 is in the first configuration, the firstswitch fabric portion 1171 and the second switch fabric portion 1173 ofeach switch fabric system 1108 function similar to the first switchfabric portion 571 and the second switch fabric portion 573, describedabove. Thus, when the switch fabric 1100 is in the first configuration,the first switch fabric portion 1171 and the second switch fabricportion 1173 operate as stand-alone three-stage switch fabrics.Accordingly, each switch fabric system 1108 acts as a stand-alone switchfabric system and is not operatively coupled to the other switch fabricsystems 1108 when the switch fabric 1100 is in the first configuration.

In the second configuration (FIG. 12), the switch fabric 1100 furtherincludes a third set of cables 1144 and multiple connection switchfabrics 1 91, each disposed within a housing 1190. The housing 1 90 canbe similar to the housing 600 described in detail above. Each switchfabric portion 1171, 1173 of each switch fabric system 1108 isoperatively coupled to each connection switch fabric 1191 via the thirdset of cables 1144. Thus, when the switch fabric 1100 is in the secondconfiguration, each switch fabric system 1108 is operatively coupled tothe other switch fabric systems 1108 via the connection switch fabrics1191. Accordingly, the switch fabric 1100 in the second configuration isa five-stage Clos network.

The third set of cables 1144 can be constructed of any material suitableto transfer data between the switch fabric portions 1171, 1173 and theconnection switch fabrics 1191. In some embodiments, for example, eachcable 1144 is constructed of multiple optical fibers. In such anembodiment, each cable 1144 can have thirty-six transmit and thirty-sixreceive fibers. The thirty-six transmit fibers of each cable 1144 caninclude thirty-two fibers for transmitting data, and four fibers forexpanding the data capacity and/or for redundancy. Similarly, thethirty-six receive fibers of each cable 1144 have thirty-two fibers fortransmitting data, and four fibers for expanding the data capacityand/or for redundancy. In other embodiments, any number of fibers can becontained within each cable. By using cables having an increased numberof optical fibers, the number of cables used can be significantlyreduced.

As discussed above, flow control can be performed within a switch fabricof, for example, a data center. FIGS. 13 and 14, and the accompanyingdescription, are schematic diagrams that illustrate flow control withina switch fabric. Specifically, FIG. 13 is a schematic diagram thatillustrates flow of data associated with a switch fabric 1300, accordingto an embodiment. The switch fabric 1300 shown in FIG. 13 is similar toswitch fabric 400 shown in FIG. 4 and can be implemented in a datacenter such as data center 100 shown in FIG. 1. In this embodiment,switch fabric 1300 is a three-stage non-blocking Clos network andincludes a first stage 1340, a second stage 1342, and a third stage1344. The first stage 1340 includes modules 1312, the second stage 1342includes modules 1314, and the third stage 1344 includes modules 1316.In some embodiments, the switch fabric 1300 can be a cell switchedswitch fabric and each module 1312 of the first stage 1340 can be a cellswitch. Each module 1312 of the first stage 1340 includes a set of inputports 1360 configured to receive data as it enters the switch fabric1300. Each module 1316 of the third stage 1344 includes output ports1362 configured to allow data to exit the switch fabric 1300. Eachmodule 1316 of the third stage 1344 includes the same number of outputports 1362.

Each module 1314 of the second stage 1342 is operatively coupled to eachmodule of the first stage 1340 by a unidirectional data path 1320. Eachunidirectional data path 1320 between each module of the first stage1340 and each module 1314 of the second stage 1342 is configured tofacilitate data transfer from the modules 1312 of the first stage 1340to the modules 1314 of the second stage 1342. Because the data paths1320 are unidirectional, they do not facilitate data transfer from themodules 1314 of the second stage 1342 to the modules 1312 of the firststage 1340. Such unidirectional data paths 1320 cost less, use fewerdata connections, and are easier to implement than similar bidirectionaldata paths.

Each module 1316 of the third stage 1344 is connected to each module1314 of the second stage 1342 by a unidirectional data path 1324. Theunidirectional data paths 1324 between the modules 1314 of the secondstage 1342 and the modules 1316 of the third stage 1344 are configuredto facilitate data transfer from the modules 1314 of the second stage1342 to the modules 1316 of the third stage 1344. Because the data paths1324 are unidirectional, they do not facilitate data transfer from themodules 1316 of the third stage 1344 to the modules 1314 of the secondstage 1344. As stated above, such unidirectional data paths 1324 costless and use less area than similar bidirectional data paths.

The unidirectional data paths 1320 between the modules 1312 of the firststage 1340 and the modules 1314 of the second stage 1342 and/or theunidirectional data paths 1320 between the modules 1314 of the secondstage 1342 and the modules 1316 of the third stage 1344 can beconstructed in any manner configured to effectively facilitate datatransfer. In some embodiments, for example, the data paths are opticalconnectors between the modules. In other embodiments, the data paths arewithin a midplane connector. Such a midplane connector can be similar tothat described in FIGS. 8 through 10. Such a midplane connector can beeffectively used to connect each module of the second stage with eachmodule of the third stage. In still other embodiments, the modules arecontained within a single chip package and the unidirectional data pathsare electrical traces.

Each module 1312 of the first stage 1340 is physically proximate to arespective module 1316 of the third stage 1344. Said another way, eachmodule 1312 of the first stage 1340 is paired with a module 1316 of thethird stage 1344. For example, in some embodiments, each module 1312 ofthe first stage 1340 is within the same chip package of a module 1316 ofthe third stage 1344. A bidirectional flow-control path 1322 existsbetween each module 1312 of the first stage 1340 and its respectivemodule 1316 of the third stage 1344. The flow-control path 1322 allows amodule 1312 of the first stage 1340 to send a flow-control indicator tothe respective module 1316 of the third stage 1344, and vice versa. Asdescribed in further detail herein, this allows any module in any stageof the switch fabric to send a flow-control indicator to the modulesending it data. In some embodiments, the bidirectional flow-controlpath 1322 is constructed of two separate unidirectional flow controlpaths. The two separate unidirectional flow control paths allowflow-control indicators to pass between a module 1312 of the first stage1340 and a module 1316 of the third stage 1344.

FIG. 14 is a schematic diagram that illustrates flow control within theswitch fabric 1300 shown in FIG. 13, according to an embodiment.Specifically, the schematic diagram illustrates a detailed view of afirst row 1310 of the switch fabric 1300 shown in FIG. 13. The first rowincludes a module 1312′ of the first stage 1340, a module 1314′ of thesecond stage 1342, and a module 1316′ of the third stage 1344. Themodule 1312′ of the first stage 1340 includes a processor 1330 and amemory 1332. The processor 1330 is configured to control receiving andtransmitting data. The memory 1332 is configured to buffer data when themodule 1314′ of the second stage 1342 cannot yet receive the data and/orthe module 1312′ of the first stage 1340 cannot yet send the data. Insome embodiments, for example, if the module 1314′ of the second stage1342 has sent a suspension indicator to the module 1312′ of the firststage 1340, the module 1312′ of the first stage 1340 buffers the datauntil the module 1314′ of the second stage 1342 can receive the data.Similarly, in some embodiments the module 1312′ of the first stage 1340can buffer data when multiple data signals are received by the module1312′ at substantially the same time (e.g., from multiple input ports).In such embodiments, if only a single data signal can be outputted fromthe module 1312′ at a given time (e.g., each clock cycle), the otherdata signals received can be buffered. Similar to the module 1312′ ofthe first stage 1340, each module in the switch fabric 1300 includes aprocessor and a memory.

The module 1312′ of the first stage 1340 and its pair module 1316′ ofthe third stage 1344 are both included on a first chip package 1326.This allows the flow-control path 1322 between the module 1312′ of thefirst stage 1340 and the module 1316′ of the third stage 1344 to beeasily constructed. For example, the flow-control path 1322 can be atrace on the first chip package 1326 between the module 1312′ of thefirst stage 1340 and the module 1316′ of the third stage. In otherembodiments, the module of the first stage and the module of the thirdstage are on separate chip packages but are in close proximity to eachother, which still allows the flow-control path between them to beconstructed without using a large amount of wiring and/or a long trace.

The module 1314′ of the second stage 1342 is included on a second chippackage 1328. The unidirectional data path 1320 between the module 1312′of the first stage 1340 and the module 1314′ of the second stage 1342,and the unidirectional data path 1324 between the module of the secondstage 1314′ and the module 1316′ of the third stage 1344 operativelyconnect the first chip package 1326 to the second chip package 1328.While not shown in FIG. 14, the module 1312′ of the first stage 1340 andthe module 1316′ of the third stage 1344 are also connected to eachmodule of the second stage by unidirectional data paths. As statedabove, the unidirectional data path can be constructed in any mannerconfigured to effectively facilitate data transfer between the modules.

The flow-control path 1322 and the unidirectional data paths 1320, 1324can be effectively used to send flow-control indicators between themodules 1312′, 1314′, 1316′. For example, if the module 1312′ of thefirst stage 1340 is sending data to the module 1314′ of the second stage1342 and the amount of data in the buffer of the module 1314′ of thesecond stage 1342 exceeds a threshold, the module 1314′ of the secondstage 1342 can send a flow-control indicator to the module 1316′ of thethird stage 1344 via the unidirectional data path 1324 between themodule 1314′ of the second stage 1342 and the module 1316′ of the thirdstage 1344. This flow-control indicator triggers the module 1316′ of thethird stage 1344 to send a flow-control indicator to the module 1312′ ofthe first stage 1340 via the flow-control path 1322. The flow-controlindicator sent from the module 1316′ of the third stage 1344 to themodule 1312′ of the first stage 1340 causes the module 1312′ of thefirst stage 1340 to stop sending data to the module 1314′ of the secondstage 1342. Similarly, flow-control indicators can be sent from themodule 1314′ of the second stage 1342 to the module 1312′ of the firststage 1340 via the module 1316′ of the third stage 1344 requesting thatdata be sent (i.e., resume sending data) from the module 1312′ of thefirst stage 1340 to the module 1314′ of the second stage 1342.

Having two stages of the switch fabric within the same chip package withan on-chip bidirectional flow-control path between them minimizes theconnections between separate chip packages, which can be bulky and/orrequire a large amount of volume. Additionally, having two stagesphysically within the same package with an on-chip bidirectionalflow-control path between them, allows the data paths between chippackages to be unidirectional while providing an ability for theflow-control communication between a sending module and a receivingmodule. More details related to bidirectional flow-control paths withina switch fabric are described in co-pending U.S. patent application Ser.No. 12/345,490, filed on Dec. 29, 2008, entitled , “Flow-Control in aSwitch Fabric,” which is incorporated herein by reference in itsentirety.

As described in connection with FIGS. 13 and 14, a buffer module can beincluded in a module within a stage of a switch fabric. More detailsrelated to a buffer module that can be included in, for example, a stageof a switch fabric are described in connection with FIG. 15.

FIG. 15 is a schematic diagram that illustrates a buffer module 1500,according to an embodiment. As shown in FIG. 15, data signals S₀ throughS_(M) are received at the buffer module 1500 on an input side 1580 ofthe buffer module 1500 (e.g., through input ports 1562 of the buffermodule 1500). After processing at the buffer module 1500, the datasignals S₀ through S_(M) are transmitted from the buffer module 1500 onan output side 1585 of the buffer module 1500 (e.g., through outputports 1564 of the buffer module 1500). Each of the data signals S₀through S_(M) can define a channel (also can be referred to as a datachannel). The data signals S₀ through S_(M) can collectively be referredto as data signals 1560. Although the input side 1580 of the buffermodule 1500 and the output side 1585 of the buffer module 1500 are shownon different physical sides of the buffer module 1500, the input side1580 of the buffer module 1500 and the output side 1585 of the buffermodule 1500 are logically defined and do not preclude various physicalconfigurations of the buffer module 1500. For example, one or more ofthe input ports 1562 and/or one or more of the output ports 1564 of thebuffer module 1500 can be physically located at any side (and/or thesame side) of the buffer module 1500.

The buffer module 1500 can be configured to process the data signals1560 such that processing latencies of the data signals 1560 through thebuffer module 1500 can be relatively small and substantially constant.Accordingly, the bit rates of the data signals 1560, as the data signals1560 are processed through the buffer module 1500, can be substantiallyconstant. For example, the processing latency of data signal S₂ throughthe buffer module 1500 can be a substantially constant number of clockcycles (e.g., a single clock cycle, a few clock cycles). Accordingly,the data signal S₂ may be time-shifted by the number of clock cycles,and the bit rate of the data signal S₂ transmitted into the input side1580 of the buffer module 1500 will be substantially the same as the bitrate of the data signal S₂ transmitted from the output side 1585 of thebuffer module 1500.

The buffer module 1500 can be configured to modify a bit rate of one ormore of the data signals 1560 in response to one or more portions offlow control signal 1570. For example, the buffer module 1500 can beconfigured to delay data signal S₂ received at the buffer module 1500 inresponse to a portion of the flow control signal 1570 indicating thatdata signal S₂ should be delayed for a specified period of time.Specifically, the buffer module 1500 can be configured to store (e.g.hold) one or more portions of the data signal S₂ until the buffer module1500 receives an indicator (e.g., a portion of flow control signal 1570)that data signal S₂ should no longer be delayed. Accordingly, the bitrate of the data signal S₂ transmitted into the input side 1580 of thebuffer module 1500 will be different (e.g., substantially different)than the bit rate of the data signal S₂ transmitted from the output side1585 of the buffer module 1500.

In some embodiments, processing at the buffer module 1500 can beperformed at memory bank based on, for example, segments ofvariable-sized cells. For example, in some embodiments, the segments ofthe cells can be processed through various memory banks (e.g., staticrandom-access memory (SRAM) memory banks) included in the buffer module1500 during a distribution process. The memory banks can collectivelydefine a shared memory buffer. In some embodiments, the segments of thedata signals can be distributed to memory banks in a predefined fashion(e.g., in a predefined pattern, in accordance with a predefinedalgorithm) during the distribution process. For example, in someembodiments, the leading segments of the data signals 1560 can beprocessed at portions of the buffer module 1500 (e.g., specified memorybanks of the buffer module 1500) that can be different than portionswhere the trailing segments are processed within the buffer module 1500.In some embodiments, the segments of the data signals 1560 can beprocessed in a particular order. In some embodiments, for example, eachof the segments of the data signals 1560 can be processed based on theirrespective positions within a cell. After the segments of the cells havebeen processed through the shared memory buffer, the segments of thecells can be ordered and sent from the buffer module 1500 during areassembly process.

In some embodiments, for example, a read multiplexing module of thebuffer module 1500 can be configured to reassemble the segmentsassociated with the data signals 1560 and send (e.g., transmit) the datasignals 1560 from the buffer module 1500. The reassembly process can bedefined based on the predefined methodology used to distribute segmentsto memory banks of the buffer module 1500. For example, the readmultiplexing module can be configured to first read a leading segmentassociated with a cell from a leading memory bank, and then readtrailing segments associated with the cell from trailing memory banks ina round-robin fashion (because the segments were written in around-robin fashion). Accordingly, very few control signals, if any,need to be transmitted between a write multiplexing module and the readmultiplexing module. More details related to segment processing (e.g.,segment distribution and/or segment reassembly) are described inco-pending U.S. patent application Ser. No. 12/415,517, filed on Mar.31, 2009, entitled, “Methods and Apparatus Related to a Shared MemoryBuffer for Variable-Sized Cells,” which has been incorporated herein byreference in its entirety.

FIG. 16A is a schematic block diagram of an ingress schedule module 1620and an egress schedule module 1630 configured to coordinatetransmissions of groups of cells via a switch fabric 1600 of a switchcore 1690, according to an embodiment. Coordinating can include, forexample, scheduling the transmission of the groups of cells via theswitch fabric 1600, tracking requests and/or responses related totransmission of the groups of cells, and so forth. The ingress schedulemodule 1620 can be included on an ingress side of the switch fabric 1600and the egress schedule module 1630 can be included on an egress side ofthe switch fabric 1600. The switch fabric 1600 can include an ingressstage 1602, a middle stage 1604, and an egress stage 1606. In someembodiments, the switch fabric 1600 can be defined based on a Closnetwork architecture (e.g., a non-blocking Clos network, a strict sensenon-blocking Clos network, a Benes network) and the switch fabric 1600can include a data plane and a control plane. In some embodiments, theswitch fabric 1600 can be a core portion of a data center (not shown),which can include a network or interconnection of devices.

As shown in FIG. 16A, ingress queues IQ₁ through IQ_(K) (collectivelyreferred to as ingress queues 1610) can be disposed on the ingress sideof the switch fabric 1600. The ingress queues 1610 can be associatedwith an ingress stage 1602 of the switch fabric 1600. In someembodiments, the ingress queues 1610 can be included in a line card. Insome embodiments, the ingress queues 1610 can be disposed outside of theswitch fabric 1600 and/or outside of the switch core 1690. Each of theingress queues 1610 can be a first-in-first-out (FIFO) type queue. Asshown in FIG. 16A, egress ports P₁ through P_(L) (collectively referredto as egress ports 1640) can be disposed on the egress side of theswitch fabric 1600. The egress ports 1640 can be associated with anegress stage 1606 of the switch fabric 1600. In some embodiments, theegress ports 1640 can be referred to as destination ports.

In some embodiments, the ingress queues 1610 can be included in one ormore ingress line cards (not shown) disposed outside of the ingressstage 1602 of the switch fabric 1600. In some embodiments, the egressports 1640 can be included in one or more egress line cards (not shown)disposed outside of the egress stage 1606 of the switch fabric 1600. Insome embodiments, one or more of the ingress queues 1610 and/or one ormore of the egress ports 1640 can be included in a one or more stages(e.g., ingress stage 1602) of the switch fabric 1600. In someembodiments, the egress schedule module 1620 can be included in one ormore egress line cards and/or the ingress schedule module 1630 can beincluded in one or more ingress line cards. In some embodiments, eachline card (e.g., egress line card, ingress line card) associated withthe switch core 1690 can include one or more schedule modules (e.g.,egress schedule module, ingress schedule module).

In some embodiments, the ingress queues 1610 and/or the egress ports1640 can be included in one or more gateway devices (not shown) disposedbetween the switch fabric 1600 and/or peripheral processing devices (notshown). The gateway device(s), the switch fabric 1600 and/or theperipheral processing devices can collectively define at least a portionof a data center (not shown). In some embodiments, the gateway device(s)can be edge devices within an edge portion of the switch core 1690. Insome embodiments, the switch fabric 1600 and the peripheral processingdevices can be configured to handle data based on different protocols.For example, the peripheral processing devices can include, for example,one or more host devices (e.g., host devices configured to execute oneor more virtual resources, a web server) that can be configured tocommunicate based on an Ethernet protocol and the switch fabric 1600,which can be a cell-based fabric. In other words, the gateway device(s)can provide the other devices configured to communicate via one protocolwith access to the switch fabric 1600, which can be configured tocommunicate via another protocol. In some embodiments, the gatewaydevice(s) can be referred to as an access switch or as a network device.In some embodiments, the gateway device(s) can be configured to functionas a router, a network hub device, and/or a network bridge device.

In this embodiment, for example, the ingress schedule module 1630 can beconfigured to define a group of cells GA queued at ingress queue IQ₁ anda group of cells GC queued at ingress queue IQ_(K-1). The group of cellsGA is queued at a front portion of the ingress queue IQ₁ and a group ofcells GB is queued within the ingress queue IQ₁ behind the group ofcells GA. Because ingress queue IQ₁ is a FIFO type queue, the group ofcells GB cannot be transmitted via the switch fabric 1600 until thegroup of cells GA have been transmitted from the ingress queue IQ₁. Thegroup of cells GC is queued at a front portion of the ingress queueIQ_(K-1).

In some embodiments, a portion of the ingress queues 1610 can be mappedto (e.g., assigned to) one or more of the egress ports 1640. Forexample, ingress queues IQ₁ through IQ_(K-1) can be mapped to egressport P₁ so that all of the queued cells 310 ingress ports IQ₁ throughIQ_(K-1) will be scheduled by the ingress schedule module 1620 fortransmission via the switch fabric 1600 to egress port P₁. Similarly,ingress queues IQ_(K) can be mapped to egress port P₂. The mapping canbe stored at a memory (e.g., memory 1622) as, for example, a look-uptable that can be accessed by ingress schedule module 1620 whenscheduling (e.g., requesting) transmission of groups of cells.

In some embodiments, one or more of the ingress queues 1610 can beassociated with a priority value (also can be referred to a transmissionpriority value). The ingress schedule module 1620 can be configured toschedule transmission of cells from the ingress queues 1610 based on thepriority values. For example, ingress schedule module 1620 can beconfigured to request transmission of group of cells GC to egress portP₁ before requesting transmission of group of cells GA to egress port P₁because ingress queue IQ_(K-1) can be associated with a higher priorityvalue than ingress queue IQ₁. The priority values can be defined basedon a level of service (e.g., a quality of service (QoS)). For example,in some embodiments, different types of network traffic can beassociated with a different level of service (and, thus a differentpriority). For example, storage traffic (e.g., read and write traffic),inter-processor communication, media signaling, session layer signaling,and so forth each can be associated with at least one level of service.In some embodiments, the priority values can be based on, for example,the IEEE 802.1 qbb protocol, which defines a priority-based flow controlstrategy.

In some embodiments, one or more of the ingress queues 1610 and/or oneor more of the egress ports 1640 can be paused. In some embodiments, oneor more of the ingress queues 1610 and/or one or more of the egressports 1640 can be paused so that cells are not dropped. For example, ifegress port P₁ is temporarily unavailable, transmission of cells fromingress queue IQ₁ and/or ingress queue IQ_(K-1) can be paused so thatcells won't be dropped at egress port P₁ because egress port P₁ istemporarily unavailable. In some embodiments, one or more of the ingressqueues 1610 can be associated with a priority value. For example, ifegress port P₁ is congested, transmission of cells from ingress queueIQ₁ to egress port P₁ can be paused rather than transmission of cellsingress queue IQ_(K-1) to egress port P₁ because ingress queue IQ_(K-1)can be associated with a higher priority value than ingress queue IQ₁.

The ingress schedule module 1620 can be configured to exchange signalswith (e.g., transmit signals to and receive signals from) the egressschedule module 1630 to coordinate the transmission of the group ofcells GA via the switch fabric 1600 to egress port P₁, and to coordinatethe transmission of group of cells GC via the switch fabric 1600 toegress port P₁. Because the group of cells GA is to be transmitted toegress port P₁, the egress port P₁ can be referred to as a destinationport of the group of cells GA. Similarly, egress port P₁ can be referredto as a destination port of the group of cells GB. As shown in FIG. 16A,the group of cells GA can be transmitted via a transmission path 4112that is different than a transmission path 4114 through which the groupof cells GC is transmitted.

The group of cells GA and the group of cells GB are defined by theingress schedule module 1620 based on cells 4110 that are queued atingress queue IQ₁. Specifically, the group of cells GA can be definedbased on each cell from the group of cells GA having a commondestination port and having a specified position within the ingressqueue IQ₁. Similarly, the group of cells GC can be defined based on eachcell from the group of cells GC having a common destination port andhaving a specified position within the ingress queue IQ_(K-1). Althoughnot shown, in some embodiments, for example, the cells 4110 can includecontent (e.g., data packets) received at the switch core 1690 from oneor more peripheral processing devices (e.g., a personal computer, aserver, a router, a personal digital assistant (PDA)) via one or morenetworks (e.g., a local area network (LAN), a wide area network (WAN), avirtual network) that can be wired and/or wireless. More details relatedto defining of groups of cells, such as group of cells GA, the group ofcells GB, and/or the group of cells GC, are discussed in connection withFIGS. 17 and 18.

FIG. 16B is a signaling flow diagram that illustrates signaling relatedto the transmission of the group of cells GA, according to anembodiment. As shown in FIG. 16B, time is increasing in a downwarddirection. After the group of cells GA has been defined (as shown inFIG. 16A), the ingress schedule module 1620 can be configured to send arequest to schedule the group of cells GA for transmission via theswitch fabric 1600; the request is shown as a transmission request 22.The transmission request 22 can be defined as a request to transmit thegroup of cells GA to egress port P₁, which is the destination port ofthe group of cells GA. In some embodiments, the destination port of thegroup of cells GA can be referred to as a target of the transmissionrequest 22 (also can be referred to as a target destination port). Insome embodiments, the transmission request 22 can include a request totransmit the group of cells GA via a particular transmission path (suchas transmission path 4112 shown in FIG. 16A) through the switch fabric1600, or at a particular time. The ingress schedule module 1620 can beconfigured to send the transmission request 22 to the egress schedulemodule 1630 after the transmission request 22 has been defined at theingress schedule module 1620.

In some embodiments, the transmission request 22 can be queued on aningress side of the switch fabric 1600 before being sent to the egressside of the switch fabric 1600. In some embodiments, the transmissionrequest 22 can be queued until the ingress schedule module 1620 triggerssending of the transmission request 22 to the egress side of the switchfabric 1600. In some embodiments, the ingress schedule module 1620 canbe configured to hold (or trigger holding of) the transmission request22 in, for example, an ingress transmission request queue (not shown)because a volume of transmission requests for sending from the ingressside of the switch fabric 1600 is higher than a threshold value. Thethreshold value can be defined based on latency of transmission via theswitch fabric 1600.

In some embodiments, the transmission request 22 can be queued at anegress queue (not shown) on an egress side of the switch fabric 1600. Insome embodiments, the egress queue can be included in a line card (notshown), can be disposed within or outside of the switch fabric 1600, orcan be disposed outside of the switch core 1690. Although not shown, insome embodiments, the transmission request 22 can be queued in an egressqueue or a portion of an egress queue associated with a specific ingressqueue (e.g., ingress queue IQ₁). In some embodiments, each of the egressports 1640 can be associated with egress queues that are associated with(e.g., correspond with) priority values of the ingress queues 1610. Forexample, egress port P₁ can be associated with an egress queue (orportion of an egress queue) associated with ingress queue IQ₁ (which canhave a specified priority value) and an egress queue (or portion of anegress queue) associated with ingress queue IQ_(K) (which can have aspecified priority value). Accordingly, a transmission request 22, whichis queued at ingress queue IQ₁, can be queued at the egress queueassociated with ingress queue IQ₁. In other words, the transmissionrequest 22 can be queued in an egress queue (on an egress side of theswitch fabric 1600) associated with a priority value of at least one ofthe ingress queues 1610. Similarly, the transmission request 22 can bequeued in an ingress transmission request queue (not shown) or portionof an ingress transmission queue associated with a priority value of theat least one of the ingress queues 1610.

If the egress schedule module 1630 determines that the destination portof the group of cells GA (i.e., egress port P₁ shown in FIG. 16A) isavailable to receive the group of cells GA, the egress schedule module1630 can be configured to send a transmission response 24 to the ingressschedule module 1620. The transmission response 24 can be, for example,an authorization for the group of cells GA to be transmitted (e.g.,transmitted from the ingress queue IQ₁ shown in FIG. 16A) to thedestination port of the group of cells GA. An authorization to transmitthe group of cells can be referred to as a transmission authorization.In some embodiments, the group of cells GA and/or the ingress queue IQ₁can be referred to as a target of the transmission response 24. In someembodiments, authorization for the group of cells GA to be transmittedcan be granted when transmission across the switch fabric 1600 issubstantially guaranteed, for example, because the destination port isavailable.

In response to the transmission response 24, the ingress schedule module1620 can be configured to transmit the group of cells GA from theingress side of the switch fabric 1600 to the egress side of the switchfabric 1600 via the switch fabric 1600. In some embodiments, thetransmission response 24 can include an instruction to transmit thegroup of cells GA via a particular transmission path (such astransmission path 4112 shown in FIG. 16A) through the switch fabric1600, or at a particular time. In some embodiments, the instruction canbe defined based on, for example, a routing policy.

As shown in FIG. 16B, the transmission request 22 includes a cellquantity value 30, a destination identifier (ID) 32, a queue identifier(ID) 34, and a queue sequence value (SV) 36 (which can collectively bereferred to as a request tag). The cell quantity value 30 can representa number of cells included in the group of cells GA. For example, inthis embodiment, the group of cells GA includes seven (7) cells (shownin FIG. 16A). The destination identifier 32 can represent thedestination port of the group of cells GA so that the target of thetransmission request 22 can be determined by the egress schedule module1630.

The cell quantity value 30 and the destination identifier 32 can be usedby the egress schedule module 1630 to schedule the group of cells GA fortransmission via the switch fabric 1600 to egress port P₁ (shown in FIG.16A). As shown in FIG. 16B, in this embodiment, the egress schedulemodule 1630 is configured to define and send the transmission response24 because the number of cells included in the group of cells GA can behandled (e.g., can be received) at the destination port of the group ofcells GA (e.g., egress port P₁ shown in FIG. 16A).

In some embodiments, if the number of cells included in the group ofcells GA cannot be handled (e.g., cannot be received) at the destinationport of the group of cells GA (e.g., egress port P₁ shown in FIG. 16A)because the destination port of the group of cells GA is unavailable(e.g., in an unavailable state, in a congested state), the egressschedule module 1630 can be configured communicate the unavailability tothe ingress schedule module 1620. In some embodiments, for example, theegress schedule module 1630 can be configured to deny the request (notshown) to transmit the group of cells GA via the switch fabric 1600 whenthe destination port of the group of cells GA is unavailable. The denialof the transmission request 22 can be referred to as a transmissiondenial. In some embodiments, the transmission denial can include aresponse tag.

In some embodiments, the availability or unavailability of, for example,egress port P₁ (shown in FIG. 16A) can be determined by the egressschedule module 1630 based on a condition being satisfied. For example,the condition can be related to a storage limit of a queue (not shown inFIG. 16A) associated with egress ports P₁ being exceeded, a flow rate ofdata via egress ports P₁, a number of cells already scheduled fortransmission from the ingress queues 1610 via the switch fabric 1600(shown in FIG. 16A), and so forth. In some embodiments, egress port P₁can be unavailable to receive cells via the switch fabric 1600 whenegress port P₁ is disabled.

As shown in FIG. 16B, the queue identifier 34 and the queue sequencevalue 36 are transmitted to the egress schedule module 1630 in thetransmission request 22. The queue identifier 34 can represent and/orcan be used to identify (e.g., uniquely identify) the ingress queue IQ₁(shown in FIG. 16A) where the group of cells GA is being queued. Thequeue sequence value 36 can represent the location of the group of cellsGA with respect to other groups of cells within the ingress queue IQ₁.For example, the group of cells GA can be associated with a queuesequence value of X and the group of cells GB (queued at ingress queueIQ₁ shown in FIG. 16A) can be associated with a queue sequence value ofY. The queue sequence value of X can indicate that the group of cells GAis to be transmitted from ingress queue IQ₁ before the group of cellsGB, which is associated with a queue sequence value of Y.

In some embodiments, the queue sequence value 36 can be selected from arange of queue sequence values associated with ingress queue IQ₁ (shownin FIG. 16A). The range of queue sequence values can be defined so thatsequence values from the range of sequence values will not be repeatedfor a specified period of time for the ingress queue IQ₁. For example,the range of queue sequence values can be defined so that queue sequencevalues from the range of queue sequence values may not be repeatedduring at least a period of time required to flush several cycles ofcells (e.g., cells 160) queued at the ingress queue IQ₁ through theswitch core 1690 (shown in FIG. 16A). In some embodiments, a queuesequence value can be incremented (within a range of queue sequencevalues) and associated with each group of cells that is defined by theingress schedule module 1620 based on cells 4110 queued at ingress queueIQ₁.

In some embodiments, the range of queue sequence values associated withthe ingress queue IQ₁ can overlap with a range of queue sequence valuesassociated with another of the ingress queues 1610 (shown in FIG. 16A).Accordingly, the queue sequence value 36, even if from a non-uniquerange of queue sequence values, can be included with (e.g., includedwithin) queue identifier 34 (which can be unique) to uniquely identifygroup of cells GA (at least during a specified period of time). In someembodiments, the queue sequence value 36 can be unique within the switchfabric 1600 or a globally unique value (GUID) (e.g., a universal uniqueidentifier (UUID)).

In some embodiments, the ingress schedule module 1620 can be configuredto wait to define a transmission request (not shown) associated withgroup of cells GB. For example, the ingress schedule module 1620 can beconfigured to wait until transmission request 22 is sent or wait until aresponse (e.g., the transmission response 24, a transmission denial) isreceived in response to transmission request 22 before defining atransmission request associated with group of cells GB.

As shown in FIG. 16B, the egress schedule module 1630 can be configuredto include the queue identifier 34 and the queue sequence value 36(which can collectively be referred to as a response tag) in thetransmission response 24. The queue identifier 34 and the queue sequencevalue 36 can be included in the transmission response 24 so that thetransmission response 24 can be associated with the group of cells GA atthe ingress schedule module 1620 when the transmission response 24 isreceived at the ingress schedule module 1620. Specifically, the queueidentifier 34 and the queue sequence value 36 can collectively be usedto identify the group of cells GA as being, for example, authorized fortransmission via the switch fabric 1600.

In some embodiments, the egress schedule module 1630 can be configuredto delay sending the transmission response 24 in response to thetransmission request 22. In some embodiments, the egress schedule module1630 can be configured to delay responding if, for example, thedestination port of the group of cells GA (i.e., egress port P₁ shown inFIG. 16A) is unavailable (e.g., temporarily unavailable). In someembodiments, the egress schedule module 1630 can be configured to sendthe transmission response 24 in response to egress port P₁ changing froman unavailable state to an available state.

In some embodiments, the egress schedule module 1630 can be configuredto delay sending the transmission response 24 because the destinationport of the group of cells GA (i.e., egress port P₁ shown in FIG. 16A)is receiving data from another of the ingress queues 1610. For example,the egress port P₁ can be unavailable to receive data from ingress queueIQ₁ because the egress port P₁ is receiving a different group of cells(not shown) from, for example, ingress queue IQ_(K) (shown in FIG. 16A).In some embodiments, groups of cells from ingress queue IQ₁ can beassociated with a higher priority value than groups of cells fromingress queue IQ_(K) based on priority values associated with ingressqueue IQ₁ and ingress queue IQ_(K). The egress schedule module 1630 canbe configured to delay sending of the transmission response 24 for atime period calculated based on, for example, a size of the differentgroup of cells being received at egress port P₁. For example, the egressschedule module 1630 can be configured to delay sending the transmissionresponse 24 targeted to group of cells GA for a projected time periodrequired to complete processing of the different group of cells ategress port P₁. In other words, the egress schedule module 1630 can beconfigured to delay sending the transmission response 24 targeted togroup of cells GA based on a projected time that the egress port P₁ willchange from an unavailable state to an available state.

In some embodiments, the egress schedule module 1630 can be configuredto delay sending the transmission response 24 because at least a portionof a transmission path (such as transmission path 4112 shown in FIG.16A) through which the group of cells GA is to be transmitted isunavailable (e.g., congested). The egress schedule module 1630 can beconfigured to delay sending of the transmission response 24 until theportion of the transmission path is no longer congested, or based on aprojected time that the portion of the transmission path will no longerbe congested.

As shown in FIG. 16B, the group of cells GA can be transmitted to thedestination port of the group of cells GA based on (e.g. in response to)the transmission response 24. In some embodiments, the group of cells GAcan be transmitted based on one or more instructions included in thetransmission response 24. For example, in some embodiments, the group ofcells GA can be transmitted via the transmission path 4112 (shown inFIG. 16A) based on an instruction included in the transmission response24, or based on one or more rules for transmission of groups of cellsvia the switch fabric 1600 (e.g., rules for transmission of groups ofcells via a rearrangable switch fabric). Although not shown, in someembodiments, after the group of cells GA has been received at egressport PI (shown in FIG. 16A), content (e.g., data packets) from the groupof cells can be transmitted to one or more network entities (e.g., apersonal computer, a server, a router, a PDA) via one or more networks(e.g., a LAN, a WAN, a virtual network) that can be wired and/orwireless.

Referring back to FIG. 16A, in some embodiments, the group of cells GAcan be transmitted via the transmission path 4112 and received at anegress queue (not shown) that can be relatively small compared with, forexample, the ingress queues 1610. In some embodiments, the egress queue(or portion of the egress queue) can be associated with a priorityvalue. The priority value can be associated with one or more of theingress queues 1610. The egress schedule module 1630 can be configuredto retrieve the group of cells GA from the egress queue and can beconfigured to transmit the group of cells GA to egress port P₁.

In some embodiments, the group of cells GA can be retrieved andtransmitted to egress port P₁ with a response identifier included withthe group of cells GA by the ingress schedule module 1620 when the groupof cells GA is transmitted to the egress side of the switch fabric 1600.The response identifier can be defined at the egress schedule module1630 and included in the transmission response 24. In some embodiments,if the group of cells GA is queued at an egress queue (not shown)associated the destination port of the group of cells GA, the responseidentifier can be used to retrieve the group of cells GA from thedestination port of the group of cells GA so that the group of cells GAcan be transmitted from the switch fabric 1600 via the destination portof the group of cells GA. The response identifier can be associated witha location in the egress queue that has been reserved by the egressschedule module 1630 for queuing of the group of cells GA.

In some embodiments, a group of cells queued at the ingress queues 1610can be moved to the memory 1622 when a transmission request (such astransmission request 22 shown in FIG. 16B) associated with the group ofcells is defined. For example, a group of cells GD queued at ingressqueue IQ_(K) can be moved to the memory 1622 in response to atransmission request associated with the group of cells GD beingdefined. In some embodiments, the group of cells GD can be moved to thememory 1622 before the transmission request associated with the group ofcells GD is sent from the ingress schedule module 1620 to the egressschedule module 1630. The group of cells GD can be stored in the memory1622 until the group of cells GD is transmitted from the ingress side ofthe switch fabric 1600 to the egress side of the switch fabric 1600. Insome embodiments, the group of cells can be moved to the memory 1622 toreduce congestion (e.g., head-of-line (HOL) blocking) at the ingressqueue IQ_(K).

In some embodiments, the ingress schedule module 1620 can be configuredto retrieve a group of cells stored in the memory 1622 based on a queueidentifier and/or a queue sequence value associated with the group ofcells. In some embodiments, the location of the group of cells withinthe memory 1622 can be determined based on a look-up table and/or anindex value. The group of cells can be retrieved before the group ofcells is transmitted from the ingress side of the switch fabric 1600 tothe egress side of the switch fabric 1600. For example, the group ofcells GD can be associated with a queue identifier and/or a queuesequence value. A location within the memory 1622 where the group ofcells GD is stored can be associated with the queue identifier and/orthe queue sequence value. A transmission request defined by the ingressschedule module 1620 and sent to the egress schedule module 1630 caninclude the queue identifier and/or the queue sequence value. Atransmission response received from the egress schedule module 1630 caninclude the queue identifier and/or the queue sequence value. Inresponse to the transmission response, the ingress schedule module 1620can be configured to retrieve the group of cells GD from the memory 1622at the location based on the queue identifier and/or the queue sequencevalue, and the ingress schedule module 1620 can trigger transmission ofthe group of cells GD.

In some embodiments, a number of cells included in a group of cells canbe defined based on an amount of space available in the memory 1622. Forexample, the ingress schedule module 1620 can be configured to definethe number of cells included in the group of cells GD based on an amountof available storage space included in the memory 1622 at the time thatthe group of cells GD is being defined. In some embodiments, the numberof cells included in the group of cells GD can be increased if theamount of available storage space included in the memory 1622 increased.In some embodiments, the number of cells included in the group of cellsGD can be increased by the ingress schedule module 1620 before and/orafter the group of cells GD is moved to the memory 1622 for storage.

In some embodiments, a number of cells included in a group of cells canbe defined based on a latency of transmission across, for example, theswitch fabric 1600. Specifically, the ingress schedule module 1620 canbe configured to define the size of a group of cells to facilitate flowacross the switch fabric 1600 in view of latencies associated with theswitch fabric 1600. For example, the ingress schedule module 1620 can beconfigured to close a group of cells (e.g., define a size of the groupof cells) because the group of cells has reached a threshold sizedefined based on the latency of the switch fabric 1600. In someembodiments, the ingress schedule module 1620 can be configured toimmediately send a data packet in a group of cells, rather than wait foradditional data packets to define a larger group of cells, because thelatency across the switch fabric 1600 is low.

In some embodiments, the ingress schedule module 1620 can be configuredto limit the number of transmission requests sent from the ingress sideof the switch fabric 1600 to the egress side of the switch fabric 1600.In some embodiments, the limit can be defined based on a policy storedat the ingress schedule module 1620. In some embodiments, a limit can bedefined based on a priority value associated with one or more of theingress queues 1610. For example, ingress schedule module 1620 can beconfigured to permit (based on a threshold limit) more transmissionrequests associated with ingress queue IQ₁ than from ingress queueIQ_(K) because ingress queue IQ₁ has a higher priority value thaningress queue IQ_(K).

In some embodiments, one or more portions of the ingress schedule module1620 and/or the egress schedule module 1630 can be a hardware-basedmodule (e.g., a DSP, FPGA) and/or a software-based module (e.g., amodule of computer code, a set of processor-readable instructions thatcan be executed at a processor). In some embodiments, one or more of thefunctions associated with the ingress schedule module 1620 and/or theegress schedule module 1630 can be included in different modules and/orcombined into one or more modules. For example, the group of cells GAcan be defined by a first sub-module within the ingress schedule module1620 and the transmission request 22 (shown in FIG. 16B) can be definedby a second sub-module within the ingress schedule module 1620.

In some embodiments, the switch fabric 1600 can have more or less stagesthan are shown in FIG. 16A. In some embodiments, the switch fabric 1600can be a reconfigurable (e.g., a rearrangeable) switch fabric and/or atime-division multiplexed switch fabric. In some embodiments, switchfabric 1600 can be defined based on a Clos network architecture (e.g., astrict sense non-blocking Clos network, a Benes network).

FIG. 17 is a schematic block diagram that illustrates two groups ofcells queued at an ingress queue 1720 disposed on an ingress side of aswitch fabric 1700, according to an embodiment. The groups of cells aredefined by an ingress schedule module 1740 on an ingress side of theswitch fabric 1700 that can be, for example, associated with a switchcore and/or included in a switch core such as that shown in FIG. 16A.The ingress queue 1720 is also on the ingress side of the switch fabric1700. In some embodiments, the ingress queue 1720 can be included in aningress line card (not shown) associated with the switch fabric 1700.Although not shown, in some embodiments, one or more of the groups ofcells can include many cells (e.g., 25 cells, 10 cells, 100 cells) oronly one cell.

As shown in FIG. 17, the ingress queue 1720 includes cells 1 through T(i.e., cell₁ through cell_(T)), which can collectively be referred to asqueued cells 1710. The ingress queue 1720 is a FIFO type queue withcell, being at the front end 1724 (or transmission end) of the queue andcell_(T) being at the back end 1722 (or entry end) of the queue. Asshown in FIG. 17, queued cells 1710 at the ingress queue 1720 include afirst group of cells 1712 and a second group of cells 1716. In someembodiments, each cell from the queued cells 1710 can have an equallength (e.g., 32 byte length, 64 byte length). In some embodiments, twoor more of the queued cells 1710 can have different lengths.

Each cell from the queued cells 1710 has content queued for transmissionto one of four egress ports 1770—egress port E, egress port F, egressport G, or egress port H—as indicated by the egress port label (e.g.,letter “E”, letter “F”) on each cell from the queued cells 1710. Theegress port 1770 to which a cell is to be transmitted can be referred toas a destination port. The queued cells 1710 can each be transmitted totheir respective destination port via the switch fabric 1700. In someembodiments, the ingress schedule module 1740 can be configured todetermine the destination port for each cell from the queued cells 1710based on, for example, a look-up table (LUT) such as a routing table. Insome embodiments, the destination port of each cell from the queuedcells 1710 can be determined based on a destination of content (e.g.,data) included in the cell. In some embodiments, one or more of theegress ports 1770 can be associated with an egress queue where cells canbe queued until transmitted via the egress ports 1770.

The first group of cells 1712 and the second group of cells 1716 can bedefined by the ingress schedule module 1740 based on the destinationports of the queued cells 1710. As shown in FIG. 17, each cell includedin the first group of cells 1712 has the same destination port (i.e.,egress port E) as indicated by the egress port labels “E.” Similarly,each cell included in the second group of cells 1716 has the samedestination port (i.e., egress port F) as indicated by the egress portlabels “F.”

The groups of cells (e.g., the first group of cells 1712) are definedbased on destination port because the groups of cells are transmittedvia the switch fabric 1700 as a group. For example, if cell₁ wereincluded in the first group of cells 1712, the first group of cells 1712could not be delivered to a single destination port because cell₁ has adifferent destination port (egress port “F”) than cell₂ through cell₇(egress port “E”). Thus, the first group of cells 1712 could not bedelivered via the switch fabric 1700 as a group.

The groups of cells are defined as continuous blocks of cells becausethe groups of cells are transmitted via the switch fabric 1700 as agroup and because the ingress queue 1720 is a FIFO type queue. Forexample, cell₁₂, and cell₂ through cell₇ could not be defined as a groupof cells because cell₂ cannot be transmitted with the block of cellscell₂ through cell₇. Cell₈ through cell₇ are intervening cells that mustbe transmitted from ingress queue 1720 after cell₂ through cell₇ aretransmitted from ingress queue 1720, but before cell₁₂ is transmittedfrom ingress queue 1720. In some embodiments, if the ingress queue 1720were not a FIFO type queue, one or more of the queued cells 1710 couldbe transmitted out of order and groups could span intervening cells.

Although not shown, each cell from the queues cells 1710 can have asequence value that can be referred to as a cell sequence value. Thecell sequence value can represent an order of, for example, cell₂ withrespect to cell₃. The cell sequence value can be used to re-order thecells at, for example, one or more of the egress ports 1770 before thecontent associated with the cells is transmitted from the egress ports1770. For example, in some embodiments, group of cells 1712 can bereceived at an egress queue (not shown) associated with egress port Eand re-ordered based on cell sequence values. In some embodiments, theegress queue can be relatively small (e.g., a shallow egress queue)compared with the ingress queue 1720.

In addition, data (e.g., data packets) that is included within the cellscan also have a sequence value that can be referred to as a datasequence value. For example, the data sequence value can represent arelative ordering of, for example, a first data packet with respect to asecond data packet. The data sequence values can be used to re-order thedata packets at, for example, one or more of the egress ports 1770before the data packets are transmitted from the egress ports 1770.

FIG. 18 is a schematic block diagram that illustrates two groups ofcells queued at an ingress queue 1820 disposed on an ingress side of aswitch fabric 1800, according to another embodiment. The groups of cellsare defined by an ingress schedule module 1840 on an ingress side of theswitch fabric 1800 that can be, for example, associated with a switchcore and/or included in a switch core such as that shown in FIG. 16A.The ingress queue 1820 is also on the ingress side of the switch fabric1800. In some embodiments, the ingress queue 1820 can be included in aningress line card (not shown) associated with the switch fabric 1800.Although not shown, in some embodiments, one or more of the groups ofcells can include only one cell.

As shown in FIG. 18, the ingress queue 1820 includes cells 1 through Z(i.e., cell₁ through cell_(Z)), which can collectively be referred to asqueued cells 1810. The ingress queue 1820 is a FIFO type queue withcell₁ being at the front end 1824 (or transmission end) of the queue andcell_(Z) being at the back end 1822 (or entry end) of the queue. Asshown in FIG. 18, queued cells 1810 at the ingress queue 1820 include afirst group of cells 1812 and a second group of cells 1816. In someembodiments, each cell from the queued cells 1810 can have an equallength (e.g., 32 byte length, 64 byte length). In some embodiments, twoor more of the queued cells 1810 can have different lengths. In thisembodiment, ingress queue 1820 is mapped to egress port F2 so that allof the cells 1810 are scheduled by the ingress schedule module 1840 fortransmission via the switch fabric 1800 to egress port F2.

Each cell from the queued cells 1810 has content associated with one ormore data packets (e.g., Ethernet data packets). The data packets arerepresented by the letters “Q” through “Y.” For example, as shown inFIG. 18, data packet R is divided into three different cells, cell₂,cell₃, and cell₄.

The groups of cells (e.g., the first group of cells 1812) are defined sothat portions of data packets are not associated with different groupsof cells. Said differently, the groups of cells are defined so thatentire data packets are associated with a single group of cells. Theboundaries of the groups of cells are defined based on boundaries of thedata packets queued at ingress queue 1820 so that the data packets arenot included in different groups of cells. Dividing data packets intodifferent groups of cells could result in undesirable consequences suchas buffering at the egress side of the switch fabric 1800. For example,if a first portion of data packet T (e.g., cell₆) was included in thefirst group of cells 1812 and second portion of data packet T (e.g.,cell₇) was included in the second group of cells 1816, the first portionof data packet T would have to be buffered in at least a portion of oneor more egress queues (not shown) at the egress side of the switchfabric 1800 until the second portion of the data packet T weretransmitted to the egress side of the switch fabric 1800 so that theentire data packet T could be transmitted from the switch fabric 1800via egress port E2.

In some embodiments, the data packets that are included within thequeued cells 1810 can also have a sequence value that can be referred toas a data sequence value. The data sequence value can represent arelative ordering of, for example, data packet R with respect to a datapacket S. The data sequence values can be used to re-order the datapackets at, for example, one or more of the egress ports 1870 before thedata packets are transmitted from the egress ports 1870.

FIG. 19 is a flowchart that illustrates a method for schedulingtransmission of a group of cells via a switch fabric, according to anembodiment. As shown in FIG. 19, an indicator that cells are queued atan ingress queue for transmission via a switch fabric is received, at1900. In some embodiments, the switch fabric can be based on a Closarchitecture and can have multiple stages. In some embodiments, theswitch fabric can be associated with (e.g., can be within) a switchcore. In some embodiments, the indicator can be received when new cellsare received at the ingress queue, or when the cells are ready (ornearly ready) to be transmitted via the switch fabric.

A group of cells that have a common destination are defined from thecells queued at the ingress queue, at 1910. The destination of each cellfrom the group of cells can be determined based on a look-up table. Insome embodiments, the destination can be determined based on a policyand/or based on a packet classification algorithm. In some embodiments,the common destination can be a common destination port associated withan ingress portion of the switch fabric.

A request tag is associated with the group of cells, at 1920. Therequest tag can include, for example, one or more of a cell quantityvalue, a destination identifier, a queue identifier, a queue sequencevalue, and so forth. The request tag can be associated with the group ofcells before the group of cells is transmitted to an ingress side of theswitch fabric.

A transmission request that includes the request tag is sent to anegress schedule module, at 1930. In some embodiments, the transmissionrequest can include a request to be transmitted at a particular time orvia a particular transmission path. In some embodiments, thetransmission request can be sent after the group of cells has beenstored in a memory associated with an ingress stage of the switchfabric. In some embodiments, the group of cells can be moved to thememory to reduce the probability of congestion at the ingress queue. Inother words, the group of cells can be moved to the memory so that othercells queued behind the group of cells can be prepared for transmission(or transmitted) from the ingress queue without waiting for the group ofcells to be transmitted from the ingress queue. In some embodiments, thetransmission request can be a request to transmit to a specified egressport (e.g., a specified destination port).

A transmission denial that includes a response tag is sent to theingress scheduling module, at 1950 when, in response to the transmissionrequest, transmission via the switch fabric is not authorized at 1940.In some embodiments, the transmission request can be denied because theswitch fabric is congested, a destination port is unavailable, and soforth. In some embodiments, the transmission request can be denied for aspecified period of time. In some embodiments, the response tag caninclude one or more identifiers that can be used to associate thetransmission denial with the group of cells.

If the transmission via the switch fabric is authorized at 1940, atransmission response that includes a response tag to the ingressscheduling module is sent, at 1960. In some embodiments, thetransmission response can be a transmission authorization. In someembodiments, the transmission response can be sent after a destinationof the group of cells is ready (or nearly ready) to receive the group ofcells.

The group of cells is retrieved based on the response tag, at 1970. Ifthe group of cells has been moved to a memory, the group of cells can beretrieved from the memory. If the group of cells is queued at theingress queue, the group of cells can be retrieved from the ingressqueue. The group of cells can be retrieved based on a queue identifierand/or a queue sequence value included in the response tag. The queueidentifier and/or the queue sequence value can be from the queue tag.

The group of cells can be transmitted via the switch fabric, at 1980.The group of cells can be transmitted via the switch fabric according toan instruction included in the transmission response. In someembodiments, the group of cells can be transmitted at a specified timeand/or via a specified transmission path. In some embodiments, the groupof cells can be transmitted via the switch fabric to a destination suchas an egress port. In some embodiments, after being transmitted via theswitch fabric, the group of cells can be queued at an egress queueassociated with a destination (e.g., destination port) of the group ofcells.

FIG. 20 is a signaling flow diagram that illustrates processing ofrequest sequence values associated with transmission requests, accordingto an embodiment. As shown in FIG. 20, a transmission request 52 istransmitted from an ingress schedule module 2020 on an ingress side of aswitch fabric to an egress schedule module 2030 on an egress side of aswitch fabric. A transmission request 56 is transmitted from the ingressschedule module 2020 to the egress schedule module 2030 after thetransmission request 52 is transmitted. As shown in FIG. 20,transmission request 54 is transmitted from ingress schedule module2030, but is not received by egress schedule module 2030. Transmissionrequest 52, transmission request 54, and transmission request 56 areeach associated with the same ingress queue IQ1 as indicated by theirrespective queue identifiers, and are associated with the samedestination port EP1 as indicated by their respective destinationidentifiers. Transmission request 52, transmission request 54 andtransmission request 56 can collectively be referred to as transmissionrequests 58. As shown in FIG. 20, time is increasing in a downwarddirection.

As shown in FIG. 20, each of the transmission requests 58 can include arequest sequence value (SV). The request sequence values can represent asequence of a transmission request with respect to other transmissionrequests. In this embodiment, the request sequence values can be from arange of request sequence values that are associated with thedestination port EP1, and are incremented in whole integers in numericalorder. In some embodiments, the request sequence values can be, forexample, strings and can be incremented in a different order (e.g.,reverse numerical order). Transmission request 52 includes a requestsequence value of 5200, transmission request 54 includes a requestsequence value of 5201, and transmission request 56 includes a requestsequence value of 5202. In this embodiment, the request sequence valueof 5200 indicates that transmission request 52 was defined and sentbefore transmission request 54, which has a request sequence value of5201.

The egress schedule module 2030 can determine that transmission of atransmission request from ingress schedule module 2020 may have failedbased on the request sequence values. Specifically, the egress schedulemodule 2030 can determine that a transmission request associated withthe request sequence value of 5201 was not received before transmissionrequest 56, which is associated with request sequence value 5202, wasreceived. In some embodiments, the egress schedule module 2030 canexecute an action with respect to the missing transmission request 54when a time period between receipt of transmission request 52 andtransmission request 56 (shown as time period 2040) exceeds a thresholdtime period. In some embodiments, egress schedule module 2030 canrequest that ingress schedule module 2020 retransmit transmissionrequest 54. The egress schedule module 2030 can include the missingrequest sequence value so that the ingress schedule module 2020 canidentify the transmission request 54 that was not received. In someembodiments, egress schedule module 2030 can deny a request fortransmission of a group of cells included in transmission request 56. Insome embodiments, the egress schedule module 2030 can be configured toprocess and/or respond to transmission requests (such as transmissionrequests 58) based on queue sequence values in a substantially similarfashion to the methods described in connection with request sequencevalues.

FIG. 21 is a signaling flow diagram that illustrates response sequencevalues associated with transmission responses, according to anembodiment. As shown in FIG. 21, a transmission response 62 istransmitted from an egress schedule module 2130 on an egress side of aswitch fabric to an ingress schedule module 2120 on an ingress side of aswitch fabric. A transmission response 66 is transmitted from the egressschedule module 2130 to the ingress schedule module 2120 after thetransmission response 62 is transmitted. As shown in FIG. 21,transmission response 64 is transmitted from egress schedule module2130, but is not received by ingress schedule module 2120. Transmissionresponse 62, transmission response 64, and transmission response 66 areassociated with the same ingress queue IQ₂ as indicated by theirrespective queue identifiers. Transmission response 62, transmissionresponse 64 and transmission response 66 can collectively be referred toas transmission responses 68. As shown in FIG. 21, time is increasing ina downward direction.

As shown in FIG. 21, each of the transmission responses 68 can includean response sequence value (SV). The response sequence values canrepresent a sequence of a transmission response with respect to othertransmission responses. In this embodiment, the response sequence valuescan be from a range of response sequence values that are associated withthe ingress queue IQ2, and are incremented in whole integers innumerical order. In some embodiments, the response sequence values canbe, for example, strings and can be incremented in a different order(e.g., reverse numerical order). Transmission response 62 includes anresponse sequence value of 5300, transmission response 64 includes anresponse sequence value of 5301, and transmission response 66 includesan response sequence value of 5302. In this embodiment, the responsesequence value of 5300 indicates that transmission response 62 wasdefined and sent before transmission response 64, which has an responsesequence value of 5301.

The ingress schedule module 2120 can determine that transmission of atransmission response from egress schedule module 2130 may have failedbased on the response sequence values. Specifically, the ingressschedule module 2120 can determine that a transmission responseassociated with the response sequence value of 5301 was not receivedbefore transmission response 66, which is associated with the responsesequence value of 5302, was received. In some embodiments, the ingressschedule module 2120 can execute an action with respect to the missingtransmission response 64 when a time period between receipt oftransmission response 62 and transmission response 66 (shown as timeperiod 2140) exceeds a threshold time period. In some embodiments,ingress schedule module 2120 can request that egress schedule module2130 retransmit transmission response 64. The ingress schedule module2120 can include the missing response sequence value so that the egressschedule module 2130 can identify the transmission response 64 that wasnot received. In some embodiments, ingress schedule module 2120 can dropa group of cells when a transmission response associated with atransmission request is not received within a specified period of time.

FIG. 22 is a schematic block diagram that illustrates multiple stages offlow-controllable queues, according to an embodiment. As shown in FIG.22, a transmit side of a first stage of queues 2210 and a transmit sideof a second stage of queues 2220 are included in a source entity 2230 ona transmit side of a physical link 2200. A receive side of the firststage of queues 2210 and a receive side of the second stage of queues2220 are included in a destination entity 2240 on a receive side of thephysical link 2200. The source entity 2230 and/or the destination entity2240 can be any type of computing device (e.g., a portion of a switchcore, a peripheral processing device) that can be configured to receiveand/or transmit data via the physical link 2200. In some embodiments,the source entity 2230 and/or the destination entity 2240 can beassociated with a data center.

As shown in FIG. 22, the first stage of queues 2210 includes transmitqueues A₁ through A₄ on the transmit side of the physical link 2200(referred to as first-stage transmit queues 2234) and receive queues D₁through D₄ on the receive side of the physical link 2200 (referred to asfirst-stage receive queues 2244). The second stage of queues 2220includes transmit queues B₁ and B₂ on the transmit side of the physicallink 2200 (referred to as second-stage transmit queues 2232) and receivequeues C₁ and C₂ on the receive side of the physical link 2200 (referredto as second-stage receive queues 2242).

Flow of data via the physical link 2200 can be controlled (e.g.,modified, suspended) based on flow control signaling associated withflow control loops between the source entity 2230 and the destinationentity 2240. For example, data transmitted from the source entity 2230on the transmit side of the physical link 2200 can be received at thedestination entity 2240 on the receive side of the physical link 2200. Aflow control signal can be defined at and/or sent from the destinationentity 2240 to the source entity 2230 when the destination entity 2240is unavailable to receive data from source entity 2230 via the physicallink 2200. The flow control signal can be configured to trigger thesource entity 2230 to modify the flow of the data from the source entity2230 to the destination entity 2240.

For example, if receive queue D₂ is unavailable to handle datatransmitted from transmit queue A₁, the destination entity 2240 can beconfigured to send a flow control signal associated with a flow controlloop to the source entity 2230; the flow control signal can beconfigured to trigger suspension of transmission of data from thetransmit queue A₁ to the receive queue D₂ via a transmission path thatincludes at least a portion of the second stage of queues 2220 and thephysical link 2200. In some embodiments, the receive queue D₂ can beunavailable, for example, when the receive queue D₂ is too full toreceive data. In some embodiments, the receive queue D2 can change froman available state to an unavailable state (e.g., a congestion state) inresponse to data previously received from the transmit queue A₁. In someembodiments, transmit queue A₁ can be referred to as a target of theflow control signal. The transmit queue A₁ can be identified within theflow control signal based on a queue identifier associated with thetransmit queue A₁. In some embodiments, the flow control signal can bereferred to as a feedback signal.

In this embodiment, a flow control loop is associated with the physicallink 2200 (referred to as a physical link control loop), a flow controlloop is associated with first the stages of queues 2210 (referred to asa first stage control loop), and a flow control loop is associated withthe second stage of queues 2220 (referred to as a second stage controlloop). Specifically, the physical link control loop is associated with atransmission path that includes the physical link 2200, and excludes thefirst stage of queues 2210 as well as the second stage of queues 2220.Flow of data via the physical link 2200 can be turned on and turned offbased on flow control signaling associated with the physical linkcontrol loop.

The first stage control loop can be based on transmission of data fromat least one of the transmit queues 2234 within the second stage ofqueues 2210 and a flow control signal defined based on an availabilityof (e.g., an indicator of an availability of) at least one of thereceive queues 2244 within the first stage of queues 2210. Thus, thefirst stage control loop can be referred to as being associated with thefirst stage of queues 2210. The first stage control loop can beassociated with a transmission path that includes the physical link2200, at least a portion of the second stage of queues 2220, and atleast a portion of the first stage of queues 2210. Flow controlsignaling associated with the first stage control loop can triggercontrol of data flow from transmit queues 2234 associated with the firststage of queues 2210.

The second stage control loop can be associated with a transmission paththat includes the physical link 2200 and includes at least a portion ofthe second stage of queues 2220, but excludes the first stage of queues2210. The second stage control loop can be based on transmission of datafrom at least one of the transmit queues 2232 within the second stage ofqueues 2220 and a flow control signal defined based on an availabilityof (e.g., an indicator of an availability of) at least one of thereceive queues 2242 within the second stage of queues 2220. Thus, thesecond stage control loop can be referred to as being associated withthe second stage of queues 2220. Flow control signaling associated withthe second stage control loop can trigger control of data flow fromtransmit queues 2232 associated with the second stage of queues 2220.

In this embodiment, the flow control loop associated with the secondstage of queues 2220 is a priority-based flow control loop.Specifically, each transmit queue from the second-stage transmit queues2232 is paired with a receive queue from the second-stage receive queues2242; and each queue pair is associated with a level of service (alsocan be referred to as a class of service or quality of service). In thisembodiment, second-stage transmit queue B₁ and second-stage transmitqueue C₁ define a queue pair and are associated with level of service X.The second-stage transmit queue B₂ and second-stage transmit queue C₂define a queue pair and are associated with service level Y. In someembodiments, different types of network traffic can be associated with adifferent level of service (and, thus a different priority). Forexample, storage traffic (e.g., read and write traffic), inter-processorcommunication, media signaling, session layer signaling, and so fortheach can be associated with at least one level of service. In someembodiments, the second stage control loop can be based on, for example,the Institute of Electrical and Electronics Engineers (IEEE) 802.1qbbprotocol, which defines a priority-based flow control strategy.

Flow of data via a transmission path 74, shown in FIG. 22, can becontrolled using at least one of the control loops. Transmission path 74includes first-stage transmit queue A₂, second-stage transmit queue B₁,the physical link 2200, second-stage receive queue C₁, and first-stagereceive queue D₃. Changes in data flow via a queue in one stage of thetransmission path 74 based on a flow control loop associated with thatstage, however, can impact data flow through another stage of thetransmission path 74. Flow control at one stage can affect data flow atanother stage because the queues (e.g., transmit queues 2232, transmitqueues 2234) within the source entity 2230 and the queues (e.g., receivequeues 2242, receive queues 2244) within the destination entity 2240 arestaged. In other words, flow control based on one flow control loop canhave an impact on flow of data via elements associated with a differentflow control loop.

For example, flow of data from first-stage transmit queue A₁ viatransmission path 74 to first-stage receive queue D₃ can be modifiedbased on one or more of the control loops—the first stage control loop,the second stage control loop, and/or the physical link control loop.Suspension of data flow to the first-stage receive queue D₃ may betriggered because the first-stage receive queue D₃ may have changed froman available state to an unavailable state (e.g., a congestion state).

If the data flowing to first-stage receive queue D₃ is associated withlevel of service X, the flow of data via second-stage transmit queue B₁and second-stage receive queue C₁ (which define the queue pairassociated with level of service X) can be suspended based on flowcontrol signaling associated with the second stage control loop (whichis a priority-based control loop). But suspending transmission of datavia the queue pair associated with level of service X can result insuspension of data transmissions from transmit queues that fan into thesecond-stage transmit queue B₁. Specifically, suspending transmission ofdata via the queue pair associated with level of service X can result insuspension of data transmissions from not only first-stage transmitqueue A₂, but also of data transmissions from first-stage transmit queueA₁. In other words, flow of data from the first-stage transmit queue A₁is indirectly or collaterally affected. In some embodiments, datareceived at transmit queue A₁ and data received at transmit queue A₂ canbe associated with the same level of service X, but the data received attransmit queue A₁ and the data received at transmit queue A₂ may befrom, for example, from different (e.g., independent) network devices(not shown) such as peripheral processing devices that can be associatedwith a different level of service.

The data flowing to first-stage receive queue D₃ can also be suspendedby specifically suspending transmission of data from the first-stagetransmit queue A₂ based on flow control signaling associated with thefirst stage control loop. By directly suspending transmission of datafrom the first-stage transmit queue A₂, data transmissions fromfirst-stage transmit queue A₁ may not be disrupted. In other words, flowcontrol of the first-stage transmit queue A₂ can be directly controlledbased on a flow control signal associated with the first stage controlloop without suspending data transmission from other first-stagetransmit queues such as the first-stage transmit queue A₁.

Flow of data to first-stage receive queue D₃ can also be controlled bysuspending transmission of data via the physical link 2200 based on flowcontrol signaling associated with the physical link control loop. Butsuspending transmission of data via the physical link 2200 can result insuspension of all data transmissions via the physical link 2200.

The queues on the transmit side of the physical link 2200 can bereferred to as transmit queues 2236 and the queues on the receive sideof the physical link can be referred to as receive queues 2246. In someembodiments, the transmit queues 2236 can also be referred to as sourcequeues, and the receive queues 2246 can be referred to as destinationqueues. Although not shown, in some embodiments, one or more of thetransmit queues 2236 can be included in one or more interface cardsassociated with the source entity 2230, and one or more of the receivequeues 2246 can be included in one or more interface cards associatedwith the destination entity 2240.

When source entity 2230 transmits data via the physical link 2200,source entity 2230 can be referred to as a transmitter disposed on atransmit side of the physical link 2200. Destination entity 2240 can beconfigured to receive the data and can be referred to as a receiverdisposed on a receive side of the physical link 2200. Although notshown, in some embodiments, the source entity 2230 (and associatedelements (e.g., transmit queues 2236)) can be configured to function asa destination entity (e.g., a receiver) and the destination entity 2240(and associated elements (e.g., receive queues 2246)) can be configuredto function as a source entity (e.g., a transmitter). Moreover, thephysical link 2200 can function as a bidirectional link.

In some embodiments, the physical link 2200 can be a tangible link suchas an optical link (e.g., a fiber optic cable, a plastic fiber cable), acable link (e.g., a copper-based wire), a twisted pair link (e.g., acategory-5 cable), and so forth. In some embodiments, the physical link2200 can be a wireless link. Data transmissions via the physical link2200 can be defined based on a protocol such as an Ethernet protocol, awireless protocol, an Ethernet protocol, a fiber channel protocol, afiber-channel-over Ethernet protocol, an Infiniband-related protocol,and/or so forth.

In some embodiments, the second stage control loop can be referred to asbeing nested within the first stage control loop because the secondstage of queues 2220, which is associated with the second stage controlloop, is disposed inside of the first stage of queues 2210, which isassociated with the first stage control loop. Similarly, the physicallink control loop can be referred to as being nested within the secondstage control loop. In some embodiments, the second stage control loopcan be referred to as an inner control loop and the first stage controlloop can be referred to as an outer control loop.

FIG. 23 is a schematic block diagram that illustrates multiple stages offlow-controllable queues, according to an embodiment. As shown in FIG.23, a transmit side of a first stage of queues 2310 and a transmit sideof a second stage of queues 2320 are included in a source entity 2330disposed on a transmit side of a physical link 2300. A receive side ofthe first stage of queues 2310 and a receive side of the second stage ofqueues 2320 are included in a destination entity 2340 disposed on areceive side of the physical link 2300. The queues on the transmit sideof the physical link 2300 can collectively be referred to as transmitqueues 2336 and the queues on the receive side of the physical link cancollectively be referred to as receive queues 2346. Although not shown,in some embodiments, the source entity 2330 can be configured tofunction as a destination entity, and the destination entity 2340 can beconfigured to function as a source entity (e.g., a transmitter).Moreover, the physical link 2300 can function as a bidirectional link.

As shown in FIG. 23, source entity 2330 is in communication withdestination entity 2340 via the physical link 2300. Source entity 2330has a queue QP1 configured to buffer data (if necessary) before the datais transmitted via the physical link 2300, and destination entity 2340has a queue QP2 configured to buffer data (if necessary) received viathe physical link 2300 before the data is distributed at the destinationentity 2340. In some embodiments, flow of data via the physical link2300 can be handled without the buffers queue QP1 and queue QP2.

Transmit queues QA₁ through QA_(N), which are included the first stageof queues 2310, can each be referred to as a first-stage transmit queueand can collectively be referred to as transmit queues 2334 (or asqueues 2334). Transmit queues QB₁ through QB_(M), which are included inthe second stage of queues 2320, can each be referred to as asecond-stage transmit queue and can collectively be referred to astransmit queues 2332 (or as queues 2332). Receive queues QD₁ throughQD_(R), which are included in the first stage of queues 2310, can eachbe referred to as a first-stage receive queue and can collectively bereferred to as receive queues 2344 (or as queues 2344). Receive queuesQC₁ through QC_(M), which are in the second stage of queues 2320, caneach be referred to as a second-stage receive queue and can collectivelybe referred to as receive queues 2342 (or as queues 2342).

As shown in FIG. 23, each queue from the second stage of queues 2320 isdisposed within a transmission path between the physical link 2300 andat least one queue from the first stage of queues 2310. For example, aportion of a transmission path can be defined by first-stage receivequeue QD₄, second-stage receive queue QC₁, and the physical link 2300.Second-stage receive queue QC₁ is disposed within the transmission pathbetween first-stage receive queue QD₄ and the physical link 2300.

In this embodiment, a physical link control loop is associated with thephysical link 2300, a first stage control loop is associated with firstthe stages of queues 2310, and a second stage control loop is associatedwith the second stage of queues 2320. In some embodiments, the secondstage control loop can be priority-based control loop. In someembodiments, the physical link control loop can include the physicallink 2300, queue QP1, and queue QP2.

Flow control signals can be defined at and/or transmitted between asource control module 2370 at the source entity 2330 and a destinationcontrol module 2380 at the destination entity 2340. In some embodiments,the source control module 2370 can be referred to as a source flowcontrol module, and the destination control module 2380 can be referredto as a destination flow control module. For example, destinationcontrol module 2380 can be configured to send a flow control signal tosource control module 2370 when one or more of the receive queues 2346(e.g., receive queue QD₂) at the destination entity 2340 is unavailableto receive data. The flow control signal can be configured to triggersource control module 2370 to, for example, suspend the flow of datafrom one or more of the receive queues 2336 to the one or more receivequeues 2346.

A queue identifier can be associated with data queued at a transmitqueue from the transmit queues 2336 by the source control module 2370before the data is transmitted. The queue identifier can representand/or can be used to identify the transmit queue where the data isbeing queued. For example, when a data packet is queued at first-stagetransmit queue QA₄, a queue identifier uniquely identifying first-stagetransmit queue QA₄ can be appended to the data packet or included in afield (e.g., a header portion, a trailer portion, a payload portion)within the data packet. In some embodiments, the queue identifier can beassociated with data at the source control module 2370, or triggered bythe source control module 2370. In some embodiments, the queueidentifier can be associated with data just before the data istransmitted, or after the data has been transmitted from one of thetransmit queues 2336.

The queue identifier can be associated with data transmitted from thetransmit side of the physical link 2300 to the receive side of thephysical link 2300 so that the source of the data (e.g., the sourcequeue) can be identified. Accordingly, a flow control signal can bedefined to suspend transmission of one or more of the transmit queues2336 based on the queue identifier. For example, a queue identifierassociated with first-stage transmit queue QA_(N) can be included in adata packet transmitted from first-stage transmit queue QA_(N) tofirst-stage receive queue QD₃. If after receiving the data packet,first-stage receive queue QD₃ is unable to receive another data packetfrom first-stage transmit queue QA_(N), a flow control signal requestingthat first-stage transmit queue QA_(N) suspend transmission ofadditional data packets to first-stage receive queue QD₃ can be definedbased on the queue identifier associated with first-stage transmit queueQA_(N). The queue identifier can be parsed from the data packet by thedestination control module 2380 and used by the destination controlmodule 2380 to define the flow control signal.

In some embodiments, data transmissions to first-stage receive queueQD_(R) from several of the transmit queues 2336 (e.g., first-stagetransmit queues 2334) can be suspended in response to the first-stagereceive queue QD_(R) changing from an available state to an unavailablestate. Each of the several transmit queues 2336 can be identified withina flow control signal based on their respective queue identifiers.

In some embodiments, one or more of the transmit queues 2336 and/or oneor more of the receive queues 2346 can be a virtual queue (e.g., alogically defined group of queues). Accordingly, a queue identifier canbe associated with (e.g., can represent) the virtual queue. In someembodiments, a queue identifier can be associated with a queue from aset of queues that define a virtual queue. In some embodiments, eachqueue identifier from a set of queue identifiers associated with thephysical link 2300 can be unique. For example, each transmit queues2336, which are associated with the physical link 2300 (e.g., associatedwith a hop), can be associated with a unique queue identifier.

In some embodiments, the source control module 2370 can be configured toassociate a queue identifier with only a specified subset of thetransmit queues 2336 and/or only a subset of data queued at one of thetransmit queues 2336. For example, if data is transmitted fromfirst-stage transmit queue QA₂ to first-stage receive queue QD₁ withouta queue identifier, a flow control signal configured to request thattransmission of data from first-stage transmit queue QA₂ be suspendedmay not be defined because the source of the data may not be known.Accordingly, a transmit queue from the transmit queues 2336 can beexempted from flow control by not associating (e.g., omitting) a queueidentifier with data when the data is transmitted from the transmitqueue.

In some embodiments, the unavailability of one or more of the receivequeues 2346 at the destination entity 2340 can be defined based on acondition being satisfied. The condition can be related to a storagelimit of a queue, a queue access rate, a flow rate of data into thequeue, and so forth. For example, a flow control signal can be definedat the destination control module 2380 in response to a status of one ormore of the receive queues 2346 such as second-stage receive queue QC₂changing from an available state to an unavailable state (e.g., acongestion state) based on a threshold storage limit being exceeded. Thesecond-stage receive queue QC₂ can be unavailable to receive data whenin the unavailable state because, for example, the second-stage receivequeue QC₂ is considered too full (as indicated by the threshold storagelimit being exceeded). In some embodiments, one or more of the receivequeue 2346 can be in an unavailable state when disabled. In someembodiments, the flow control signal can be defined based on a requestto suspend transmission of data to a receive queue from the receivequeues 2346 when the receive queue is unavailable to receive data. Insome embodiments, the status of one or more of the receive queues 2346can be changed from an available state to a congestion state (bydestination control module 2380) in response to a specified subset ofreceive queues 2346 (e.g., receive queues within a specified stage)being in a congestion state.

In some embodiments, a flow control signal can be defined at thedestination control module 2380 to indicate that one of the receivequeues 2346 has changed from an unavailable state to an available state.For example, initially, the destination control module 2380 can beconfigured to define and send a first flow control signal to the sourcecontrol module 2370 in response to first-stage receive queue QD₃changing from an available state to an unavailable state. Thefirst-stage receive queue QD₃ can change from the available state to theunavailable state in response to data sent from first-stage transmitqueue QA₂. Accordingly, the target of the first flow control signal canbe first-stage transmit queue QA₂ (as indicated based on a queueidentifier). When the first-stage receive queue QD₃ changes from theunavailable state back to the available state, the destination controlmodule 2380 can be configured to define and send a second flow controlsignal to the source control module 2370 indicating the change from theunavailable state back to the available state. In some embodiments, thesource control module 2370 can be configured to trigger transmission ofdata from one or more of the transmit queues 2336 to the first-stagereceive queue QD₃ in response to the second flow control signal.

In some embodiments, a flow control signal can have one or moreparameter values that can be used by the source control module 2370 tomodify transmission from one of the transmit queues 2336 (identifiedwithin the flow control signal by a queue identifier). For example, aflow control signal can include a parameter value that can trigger thesource control module 2370 to suspend transmission from one of thetransmit queues 2336 for a specified period of time (e.g., 10milliseconds (ms)). In other words, the flow control signal can includea suspension-time-period parameter value. In some embodiments, thesuspension time period can be indefinite. In some embodiments, the flowcontrol signal can define a request to transmit data from one or more ofthe transmit queues 2336 at a specified rate (e.g., specified number offrames per second, specified number of bytes per second).

In some embodiments, a flow control signal (e.g., the suspension timeperiod within the flow control signal) can be defined based on a flowcontrol algorithm. The suspension time period can be defined based on atime period during which a receive queue from the receive queues 2346(e.g., first-stage receive queue QD₄) will be unavailable. In someembodiments, the suspension time period can be defined based on morethan one of the first stage receive queues 2344 being unavailable. Forexample, in some embodiments, the suspension time period can beincreased when more or less than a specified number of the first stagereceive queues 2344 is in a congestion state. In some embodiments, thistype of determination can be made at the destination control module2380. The time period during which the receive queue will be unavailablecan be a projected (e.g., predicted) time period calculated by thedestination control module 2380 based on, for example, a flow rate(e.g., a historic flow rate, a prior flow rate) of data from the receivequeue.

In some embodiments, the source control module 2370 can deny or alter arequest to modify the flow of data from one or more of the transmitqueues 2336. For example, in some embodiments, the source control module2370 can be configured to decrease or increase a suspension time period.In some embodiments, rather than suspend transmission of data inresponse to a flow control signal, the source control module 2370 can beconfigured to modify a transmission path associated with one of thetransmission queues 2336. For example, if first-stage transmit queue QA₂has received a request to suspend transmission based on a change instatus of first-stage receive queue QD₂, the source control module 2370can be configured to trigger transmission of data from first-stagetransmit queue QA2 to, for example, first-stage receive queue QD₃ ratherthan comply with the request to suspend transmission.

As shown in FIG. 23, queues within the second stage of queues 2320 faninto or fan out of the physical link 2300. For example, transmit queues2332 (i.e., queues QB₁ through QB_(M)) on the transmit side of thephysical link 2300 fan into queue QP1 on the transmit side of physicallink 2300. Accordingly, data queued at any of the transmit queues 2332can be transmitted to queue QP1 of the physical link 2300. On thereceive side of the physical link 2300, data transmitted from thephysical link 2300 via queue QP2 can be broadcast to receive queues 2342(i.e., queues QC₁ through QC_(M)).

Also, as shown in FIG. 23, transmit queues 2334 within a first stage ofqueues 2310 fan into the transmit queues 2332 within the second stage ofqueues 2320. For example, data queued at any of the first-stage transmitqueues QA₁, QA₄, and QA_(N-2) can be transmitted to second-stagetransmit queue QB₂. On the receive side of the physical link 2300, datatransmitted from, for example, second-stage receive queue QC_(M) can bebroadcast to first-stage receive queues QD_(R-1) and QD_(R).

Because many of the flow control loops (e.g., first control loop) areassociated with different fan-in and fan-out architectures, the flowcontrol loops can have various affects on the flow of data via thephysical link 2300. For example, when transmission of data from thesecond-stage transmit queue QB₁ is suspended based on the second stagecontrol loop, transmission of data from first-stage transmit queues QA₁,QA₂, QA₃, and QA_(N-1) via the second-stage transmit queue QB₁ to one ormore of the receive queues 2346 is also suspended. In this case,transmission of data from one or more upstream queues (e.g., first-stagetransmit queue QA₁) can be suspended when transmission from a downstreamqueue (e.g., second-stage transmit queue QB₁) is suspended. In contrast,if transmission of data from first-stage transmit queue QA₁ along atransmission path that includes at least downstream second-stagetransmit queue QB₁ is suspended based on the first stage control loop, aflow rate of data from the second-stage transmit queue QB₁ may bedecreased without entirely suspending transmission of data fromsecond-stage transmit queue QB₁; first-stage transmit queue QA₁, forexample, may still be able to transmit data via second-stage transmitqueue QB₁.

In some embodiments, the fan-in and fan-out architecture can bedifferent than that shown in FIG. 23. For example, in some embodiments,some of the queues within the first stage of queues 2310 can beconfigured to fan into the physical link 2300, bypassing the secondstage of queues 2320.

Flow control signaling associated with the transmit queues 2336 ishandled by the source control module 2370 and flow control signalingassociated with the receive queues 2346 is handled by the destinationcontrol module 2380. Although not shown, in some embodiments, flowcontrol signaling can be handled by one or more control modules (orcontrol sub-modules) that can be separate and/or integrated into asingle control module. For example, flow control signaling associatedwith the first-stage receive queues 2344 can be handled by a controlmodule separate from a control module configured to handle flow controlsignaling associated with the second-stage receive queues 2342.Likewise, flow control signaling associated with the first-stagetransmit queues 2334 can be handled by a control module separate from acontrol module configured to handle flow control signaling associatedwith the second-stage transmit queues 2332. In some embodiments, one ormore portions of the source control module 2370 and/or the destinationcontrol module 2380 can be a hardware-based module (e.g., a DSP, a FPGA)and/or a software-based module (e.g., a module of computer code, a setof processor-readable instructions that can be executed at a processor).

FIG. 24 is a schematic block diagram that illustrates a destinationcontrol module 2450 configured to define a flow control signal 6428associated with multiple receive queues, according to an embodiment. Thestages of queues include a first stage of queues 2410 and a second stageof queues 2420. As shown in FIG. 24, a source control module 2460 isassociated with a transmit side of the first stage of queues 2410 and adestination control module 2450 is associated with a receive side of thefirst stage of queues 2410. The queues on the transmit side of aphysical link 2400 can collectively be referred to as transmit queues2470. The queues on the receive side of the physical link 2400 cancollectively be referred to as receive queues 2480.

The destination control module 2450 is configured to send the flowcontrol signal 6428 to the source control module 2460 in response to oneor more receive queues within the first stage of queues 2410 beingunavailable to receive data from a single source queue at the firststage of queues 2410. The source control module 2460 can be configuredto suspend transmission of data from the source queue at the first stageof queues 2410 to the multiple receive queues at the first stage ofqueues 2410 based on the flow control signal 6428.

The flow control signal 6428 can be defined by the destination controlmodule 2450 based on information associated with each unavailablereceive queue within the first stage of queues 2410. The destinationcontrol module 2450 can be configured to collect the informationassociated with the unavailable receive queues and can be configured todefine the flow control signal 6428 so that potentially conflicting flowcontrol signals (not shown) will not be sent to the single source queueat the first stage of queues 2410. In some embodiments, the flow controlsignal 6428 defined based on the collection of information can bereferred to as an aggregated flow control signal.

Specifically, in this example, the destination control module 2450 isconfigured to define the flow control signal 6428 in response to tworeceive queues—receive queue 2442 and receive queue 2446—at the receiveside of the first stage of queues 2410 being unavailable to receive datafrom a transmit queue 2412 on the transmit side of the first stage ofqueues 2410. In this embodiment, receive queue 2442 and receive queue2446 are changed from an available state to an unavailable state inresponse to data packets sent from transmit queue 2412 via transmissionpath 6422 and transmission path 6424, respectively. As shown in FIG. 24,transmission path 6422 includes transmit queue 2412, transmit queue 2422within a second stage of queues 2420, the physical link 2400, receivequeue 2432 within the second stage of queues 2420, and receive queue2442. Transmission path 6424 includes transmit queue 2412, transmitqueue 2422, the physical link 2400, receive queue 2432, and receivequeue 2446.

In some embodiments, a flow control algorithm can be used to define theflow control signal 6428 based on information related to theunavailability of receive queue 2442 and/or information related to theunavailability of receive queue 2446. For example, if destinationcontrol module 2450 determines that receive queue 2442 and that receivequeue 2446 will be unavailable for different time periods, thedestination control module 2450 can be configured to define the flowcontrol signal 6428 based on the different time periods. For example,the destination control module 2450 can request, via the flow controlsignal 6428, that transmission of data from transmit queue 2412 besuspended for a time period calculated based on the different timeperiods (e.g., a time period equal to an average of the different timeperiods, a time period equal to the greater of the time differentperiods). In some embodiments, the flow control signal 6428 can bedefined based on individual suspension requests from the receive side ofthe first stage of queues 2410 (e.g., a suspension request associatedwith receive queue 2442 and a suspension request associated with receivequeue 2446).

In some embodiments, the flow control signal 6428 can be defined basedon a maximum or a minimum allowable time period. In some embodiments,the flow control signal 6428 can be calculated based on an aggregateflow rate of data from, for example, transmit queue 2412. For example,the suspension time period can be scaled based on the aggregate flowrate of data from transmit queue 2412. In some embodiments, for example,the suspension time period can be increased if the flow rate of datafrom transmit queue 2412 is larger than a threshold value, and thesuspension time period can be decreased if the flow rate of data fromtransmit queue 2412 is lower than a threshold value.

In some embodiments, the flow control algorithm can be configured towait for a specified period of time before defining and/or sending theflow control signal 6428. The wait time period can be defined so thatmultiple suspension requests related to transmit queue 2412 and, whichcan be received at different times within the wait time period, can beused to define the flow control signal 6428. In some embodiments, thewait period can be triggered in response to at least one suspensionrequest related to transmit queue 2412 being received.

In some embodiments, the flow control signal 6428 can be defined by aflow control algorithm based on a priority value associated with eachreceive queue within the first stage of queues 2410. For example, ifreceive queue 2442 has a priority value that is higher than a priorityvalue associated with receive queue 2446, the destination control module2450 can be configured to define the flow control signal 6428 based oninformation associated with receive queue 2442 rather than receive queue2446. For example, the flow control signal 6428 can be defined based ona suspension time period associated with receive queue 2442 rather thana suspension time period associated with receive queue 2446 becausereceive queue 2442 can have a higher priority value than a priorityvalue associated with receive queue 2446.

In some embodiments, the flow control signal 6428 can be defined by aflow control algorithm based on an attribute associated with eachreceive queue within the first stage of queues 2410. For example, theflow control signal 6428 can be defined based on receive queue 2442and/or receive queue 2446 being a specified type of queue (e.g., alast-in-first-out (LIFO) queue, a first-in-first-out (FIFO) queue). Insome embodiments, the flow control signal 6428 can be defined based onreceive queue 2442 and/or receive queue 2446 being configured to receivea specified type of data (e.g., a control data/signal queue, a mediadata/signal queue).

Although not shown, one or more control modules associated with a stageof queues (e.g., the first stage of queues 2410) can be configured tosend information to a different control module where the information canbe used to define a flow control signal. The different control modulecan be associated with a different stage of queues. For example, asuspension request associated with receive queue 2442 and a suspensionrequest associated with receive queue 2446 can be defined at destinationcontrol module 2450. The suspension requests can be sent to adestination control module (not shown) associated with a receive side ofthe second stage of queues 2420. A flow control signal (not shown) canbe defined at the destination control module associated with the receiveside of the second stage of queues 2420 based on the suspension requestsand based on a flow control algorithm.

The flow control signal 6428 can be defined based on a flow control loopassociated with the first stage of queues 2410 (e.g., a first stagecontrol loop). One or more flow control signals (not shown) can also bedefined based on a flow control loop associated with the second stage ofqueues 2420 and/or a flow control loop associated with the physical link2400.

Transmission of data associated with transmit queues within the firststage of queues 2410 (other than transmit queue 2412) is substantiallyunrestricted by flow control signal 6428 because flow of data to thereceive queues 2442 and 2446 is controlled based on the first stage flowcontrol loop. For example, transmit queue 2414 can continue to transmitdata via transmit queue 2422 even though transmission of data fromtransmit queue 2412 is suspended. For example, transmit queue 2414 canbe configured to transmit data via transmission path 6426, whichincludes transmit queue 2422, to receive queue 2448 even thoughtransmission of data from transmit queue 2412 via transmit queue 2422has been suspended. In some embodiments, transmit queue 2422 can beconfigured to continue to transmit data to receive queue 2442 from, forexample, transmit queue 2416 even though transmission of data from queue2412 via transmission path 6422 has been suspended based on flow controlsignal 6428.

If transmission of data to the receive queues 2442 and 2446 were insteadsuspended by controlling flow of data via transmit queue 2422 based on aflow control signal (not shown) associated with the second stage controlloop, transmission of data from transmit queue 2414 and transmit queue2416 via transmit queue 2422 would also be restricted (in addition totransmission of data from transmit queue 2412). Transmission of datafrom transmit queue 2422 could be suspended because it is associatedwith a specified level of service, and the data that caused, forexample, congestion at receive queues 2442 and 2446 may be associatedwith that specified level of service.

One or more parameter values defined within the flow control signal 6428can be stored at a memory 2452 of the destination control module 2450.In some embodiments, the parameter value(s) can be stored at the memory2452 of the destination control module 2450 after they have been definedand/or when the flow control signal 6428 is sent to the source controlmodule 2460. A parameter value defined within the flow control signal6428 can be used to track a state of, for example, transmit queue 2412.For example, an entry within the memory 2452 can indicate that thetransmit queue 2412 is in a suspended state (e.g., a non-transmitstate). The entry can be defined based on a suspension-time-periodparameter value defined within the flow control signal 6428. When thesuspension time period has expired, the entry can be updated to indicatethat the state of the transmit queue 2412 has changed to, for example,an active state (e.g., a transmit state). Although not shown, in someembodiments, the parameter value(s) can be stored at a memory (e.g., aremote memory) outside of the destination control module 2450.

In some embodiments, the parameter value(s) (e.g., state informationdefined based on the parameter value(s)) stored at the memory 2452 ofthe destination control module 2450 can be used by the destinationcontrol module 2450 to determine whether or not an additional flowcontrol signal (not shown) should be defined. In some embodiments, theparameter value(s) can be used by the destination control module 2450 todefine one or more additional flow control signals.

For example, if receive queue 2442 is changed from an available state toan unavailable (e.g., a congestion state) in response to a first datapacket received from transmit queue 2412, a request to suspendtransmission of data from transmit queue 2412 can be communicated viathe flow control signal 6428. The flow control signal 6428 can indicate,based on a queue identifier, that transmit queue 2412 is a target of therequest and can specify a suspension time period. The suspension timeperiod and the queue identifier associated with transmit queue 2412 canbe stored in the memory 2452 of the destination control module 2450 whenthe flow control signal 6428 is sent to the source control module 2460.After the flow control signal 6428 is sent, receive queue 2444 can bechanged from an available state to a congestion state in response to asecond data packet received from transmit queue 2412 (transmission pathis not shown in FIG. 24). The second data packet can be sent from thetransmit queue 2412 before transmission of data from the transmit queue2412 is suspended based on flow control signal 6428. The destinationcontrol module 2450 can access the information stored in the memory 2452and can determine that an additional flow control signal targeted totransmit queue 2412 should not be defined and sent to the source controlmodule 2460 in response to the change in state associated with receivequeue 2444 because flow control signal 6428 has already been sent.

In some embodiments, the source control module 2460 can be configured tosuspend transmission from transmit queue 2412 based on the most recentflow control signal parameter values. For example, after the flowcontrol signal 6428, which is targeted to transmit queue 2412, has beensent to the source control module 2460, a later flow control signal (notshown) targeted to transmit queue 2412 can be received at the sourcecontrol module 2460. The source control module 2460 can be configured toimplement one or more parameter values associated with the later flowcontrol signal rather than parameter values associated with flow controlsignal 6428. In some embodiments, the later flow control signal cantrigger the transmit queue 2412 to remain in a suspended state for alonger or shorter period of time than indicated in the flow controlsignal 6428.

In some embodiments, the source control module 2460 can optionallyimplement one or more of the parameter values associated with the laterflow control signal when a priority value associated with the parametervalue(s) is higher (or lower) than a priority value associated with oneor more of the parameter values associated with flow control signal6428. In some embodiments, each priority value can be defined at thedestination control module 2450 and each priority value can be definedbased on a priority value associated with one or more of the receivequeues 2480.

In some embodiments, the flow control signal 6428 and the later flowcontrol signal (which are both targeted to transmit queue 2412) can bothbe defined in response to the same receive queue from the receive queues2480 being unavailable. For example, the later flow control signal caninclude updated parameter values defined by the destination controlmodule 2450 based on receive queue 2442 remaining in an unavailablestate for a longer period of time than previously calculated. In someembodiments, the flow control signal 6428 targeted to transmit queue2412 can be defined in response to one of the receive queues 2480changing state (e.g., changing from an available state to an unavailablestate), and the later flow control signal targeted to transmit queue2412 can be defined in response to another of the receive queues 2480changing state (e.g., changing from an available state to an unavailablestate).

In some embodiments, multiple flow control signals can be defined at thedestination control module 2450 to suspend transmissions from multipletransmit queues from the first stage of queues 2410. In someembodiments, the multiple transmit queues can be transmitting data to asingle receive queue such as receive queue 2444. In some embodiments, ahistory of the flow control signals to the multiple transmit queues fromthe first stage of queues 2410 can be stored in the memory 2452 of thedestination control module 2450. In some embodiments, a later flowcontrol signal associated with the single receive queue can becalculated based on the history of the flow control signals.

In some embodiments, suspension time periods that are associated withmultiple transmit queues can be grouped and included in a flow controlpacket. For example, a suspension time period associated with transmitqueue 2412 and a suspension time period associated with transmit queue2414 can be included in a flow control packet (also can be referred toas a flow control packet). More details related to a flow control packetare described in connection with FIG. 25.

FIG. 25 is a schematic diagram that illustrates a flow control packet,according to an embodiment. The flow control packet includes a header2510, a trailer 2520, and a payload 2530 that includessuspension-time-period parameter values (shown in column 2512) forseveral transmit queues represented by queue identifiers (IDs) (shown incolumn 2514). As shown in FIG. 25, transmit queues represented by queueIDs 1 through V (i.e., Queue ID₁ through Queue ID_(V)) are eachassociated with a suspension-time-period parameter value 1 through V(i.e., Suspension Time Period₁ through Suspension Time Period_(V)). Thesuspension-time-period parameter values 2514 indicate time periodsduring which transmit queues represented by the queue IDs 2512 should besuspended (e.g., prohibited) from transmitting data.

In some embodiments, the flow control packet can be defined at, forexample, a destination control module such as destination control module2450 shown in FIG. 24. In some embodiments, the destination controlmodule can be configured to define a flow control packet at regular timeintervals. For example, the destination control module can be configuredto define a flow control packet every 10 ms. In some embodiments, thedestination control module can be configured to define a flow controlpacket at random times, when a suspension-time-period parameter valuehas been calculated, and/or when a specified number ofsuspension-time-period parameter values have been calculated. In someembodiments, the destination control module can determine that at leasta portion of the flow control packet should not be defined and/or sent,for example, based on one or more parameter values and/or stateinformation accessed by the destination control module.

Although not shown, in some embodiments, multiple queue IDs can beassociated with a single suspension-time-period parameter value. In someembodiments, at least one queue ID can be associated with a parametervalue other than a suspension-time-period parameter value. For example,a queue ID can be associated with a flow rate parameter value. The flowrate parameter value can indicate a flow rate (e.g., a maximum flowrate) at which transmit queues (represented by the queue IDs) shouldtransmit data. In some embodiments, the flow control packet can have oneor more fields configured to indicate whether or not a particularreceive queue is available to receive data.

The flow control packet can be communicated from the destination controlmodule to a source control module (such as source control module 2460shown in FIG. 24) via a flow control signal (such as flow control signal6428 shown in FIG. 24). In some embodiments, the flow control packet canbe defined based on a layer-2 (e.g., layer-2 of the OSI model) protocol.In other words, the flow control packet can be defined at and usedwithin layer-2 of a network system. In some embodiments, the flowcontrol packet can be transmitted between devices associated withlayer-2 (e.g., a MAC device).

Referring back to FIG. 25, one or more parameter values (e.g., stateinformation defined based on the parameter value(s)) associated with theflow control signal 6428 can be stored in a memory 2562 of the sourcecontrol module 2560. In some embodiments, the parameter value(s) can bestored at the memory 2562 of the source control module 2560 when theflow control signal 6428 is received at the source control module 2560.A parameter value defined within the flow control signal 6428 can beused to track a state of one or more of the receive queues 2580 (e.g.,receive 2542). For example, an entry within the memory 2562 can indicatethat receive queue 2542 is unavailable to receive data. The entry can bedefined based on a suspension-time-period parameter value defined withinthe flow control signal 6428 and associated with an identifier (e.g., aqueue identifier) of the receive queue 2542. When the suspension timeperiod has expired, the entry can be updated to indicate that the stateof the receive queue 2542 has changed to, for example, an active state.Although not shown, in some embodiments, the parameter value(s) can bestored at a memory (e.g., a remote memory) outside of the source controlmodule 2560.

In some embodiments, the parameter value(s) (and/or state information)stored at the memory 2562 of the source control module 2560 can be usedby the source control module 2560 to determine whether or not datashould be transmitted to one or more of the receive queues 2580. Forexample, the source control module 2560 can be configured to transmitdata from transmit queue 2516 to receive queue 2544 rather than receivequeue 2542 based on state information related to receive queue 2544 andreceive queue 2542.

In some embodiments, the source control module 2560 can analyze datatransmission patterns to determine whether or not data should betransmitted from one or more of the source queues 2570 to one or more ofthe receive queues 2580. For example, the source control module 2560 candetermine based on parameter values stored at the memory 2562 of thesource control module 2560 that transmit queue 2514 is sending arelatively high volume of data to receive queue 2546. Based on thisdetermination the source control module 2560 can trigger queue 2516 totransmit data to receive queue 2548 rather than receive queue 2546because receive queue 2546 is receiving the high volume of data fromtransmit queue 2514. By analyzing transmission patterns associated withthe transmit queues 2570 the onset of congestion at one or more of thereceive queues 2580 can be substantially avoided.

In some embodiments, the source control module 2560 can analyzeparameter values (and/or state information) stored at the memory 2562 ofthe source control module 2560 to determine whether or not data shouldbe transmitted to one or more of the receive queues 2580. By analyzingstored parameter values (and/or state information), the onset ofcongestion at one or more of the transmit queues 2580 can besubstantially avoided. For example, the source control module 2560 cantrigger data to be transmitted to receive queue 2540 rather than receivequeue 2542 based on the historical availability of receive queue 2540compared with (e.g., being better than, being worse than) the historicalavailability of receive queue 2542. In some embodiments, for example,the source control module 2560 can transmit data to receive queue 2542rather than receive queue 2544 based on the historical performance ofreceive queue 2542 compared with the historical performance of receivequeue 2544 with respect to data bursts patterns. In some embodiments,the analysis of parameter values related to one or more of the receivequeues 2580 can be based on a particular time window, a particular typeof network transaction (e.g., inter-processor communication), aparticular level of service, and so forth.

In some embodiments, the destination control module 2550 can send statusinformation (e.g., current status information) about the receive queues2580 that can be used by the source control module 2560 to determinewhether or not data should be transmitted from one or more of the sourcequeues 2570. For example, the source control module 2560 can triggerqueue 2514 to transmit data to queue 2544 rather than queue 2546 becausequeue 2546 has more available capacity than queue 2544 as indicated bythe destination control module 2550. In some embodiments, anycombination of current status information, transmission patternanalysis, and historical data analysis can be used to substantiallyprevent, or reduce the likelihood of the onset of congestion of one ormore of the receive queues 2580.

In some embodiments, the flow control signal 6428 can be sent from thedestination control module 2550 to the source control module 2560 via anout-of-band transmission path. For example, the flow control signal 6428can be sent via a link dedicated to communications related to flowcontrol signaling. In some embodiments, the flow control signal 6428 canbe transmitted via queues associated with the second stage of queues2520, queues associated with the first stage of queues 2510, and/or thephysical link 2500.

Some embodiments described herein relate to a computer storage productwith a computer-readable medium (also can be referred to as aprocessor-readable medium) having instructions or computer code thereonfor performing various computer-implemented operations. The media andcomputer code (also can be referred to as code) may be those designedand constructed for the specific purpose or purposes. Examples ofcomputer-readable media include, but are not limited to: magneticstorage media such as hard disks, floppy disks, and magnetic tape;optical storage media such as Compact Disc/Digital Video Discs(CD/DVDs), Compact Disc-Read Only Memories (CD-ROMs), and holographicdevices; magneto-optical storage media such as optical disks; carrierwave signal processing modules; and hardware devices that are speciallyconfigured to store and execute program code, such as ASICs,Programmable Logic Devices (PLDs), and Read-Only Memory (ROM) and RAMdevices.

Examples of computer code include, but are not limited to, micro-code ormicro-instructions, machine instructions, such as produced by acompiler, code used to produce a web service, and files containinghigher-level instructions that are executed by a computer using aninterpreter. For example, embodiments may be implemented using Java,C++, or other programming languages (e.g., object-oriented programminglanguages) and development tools. Additional examples of computer codeinclude, but are not limited to, control signals, encrypted code, andcompressed code.

While various embodiments have been described above, it should beunderstood that they have been presented by way of example only, notlimitation, and various changes in form and details may be made. Anyportion of the apparatus and/or methods described herein may be combinedin any combination, except mutually exclusive combinations. Theembodiments described herein can include various combinations and/orsub-combinations of the functions, components and/or features of thedifferent embodiments described.

1. An apparatus, comprising; a switch core having a multi-stage switchfabric, the multi-stage switch fabric having a plurality of ingressports and a plurality of egress ports, the switch core configured to becoupled to a plurality of edge devices via the plurality of ingressports and the plurality of egress ports, the switch core configured toreceive a packet from an ingress port from the plurality of ingressports, the switch core configured to send a plurality of cellsassociated with the packet from the ingress port to an egress port fromthe plurality of egress ports without a store-and-forward delayassociated with a zero-load latency for the switch core and such that alatency for each cell from the plurality of cells is independent of apath within the multi-stage switch fabric of the switch core traversedby that cell.
 2. The apparatus of claim 1, wherein: the plurality ofingress ports numbers at least 1,000 ports, and the plurality of egressports numbers at least 1,000 ports.
 3. The apparatus of claim 1,wherein: the switch core is configured to include symmetrical cablingtopology.
 4. The apparatus of claim 1, wherein: the switch coreconfigured to send the plurality of cells from the ingress port to theegress port such at the zero-load latency excluding speed-of-lightlatency or a congestion latency excluding speed-of-light latency is lessthan 15 μsec.
 5. The apparatus of claim 1, wherein: the switch coreconfigured to send the plurality of cells from the ingress port to theegress port such at the zero-load latency excluding speed-of-lightlatency or a congestion latency excluding speed-of-light latency is lessthan 10 μsec.
 6. The apparatus of claim 1, wherein: the switch core isconfigured such that the zero-load latency excluding speed-of-lightlatency and a congestion latency excluding speed-of-light latency eachis independent of a location of the ingress port and a location of theegress port, the multi-stage switch fabric is configured to send theplurality of cells associated with the packet from the ingress port tothe egress port substantially without loss.
 7. The apparatus of claim 1,wherein: the egress port is a first egress port, a latency associatedwith a second egress port from the plurality of egress port beingindependent from a latency associated with the first egress port whenthe first egress port is congested.
 8. The apparatus of claim 1,wherein: the egress port is included in a first subset of egress portsfrom the plurality of egress ports, a latency associated with eachegress port from a second subset of egress ports from the plurality ofegress ports being independent from a latency associated with eachegress port from the first subset of egress ports when each egress portfrom the first subset of egress ports is congested, the first subset ofegress ports being mutually exclusive from the second subset of egressports.
 9. An apparatus, comprising; a switch core having a multi-stageswitch fabric, the multi-stage switch fabric having a plurality ofingress ports and a plurality of egress ports, the switch coreconfigured to be coupled to a plurality of edge devices via theplurality of ingress ports and the plurality of egress ports, the switchcore configured to receive a packet from each ingress port from theplurality of ingress ports, the switch core configured to send aplurality of cells associated with each packet from the associatedingress port to an associated egress port from the plurality of egressports such that a latency for each cell is independent of a path withinthe multi-stage switch fabric of the switch core traversed by that cellwhen a cabling topology of the switch core is symmetrical and when linkof the cabling topology are fully operational.
 10. The apparatus ofclaim 9, wherein: the plurality of ingress ports numbers at least 1,000ports, and the plurality of egress ports numbers at least 1,000 ports.11. The apparatus of claim 9, wherein the switch core is configured tosend the plurality of cells associated with the packet from the ingressport to the egress port without a store-and-forward delay associatedwith a zero-load latency for the switch core.
 12. The apparatus of claim9, wherein: the switch core is configured such that the zero-loadlatency excluding speed-of-light latency and the congestion latencyexcluding speed-of-light latency each is independent of a location ofthe ingress port and a location of the egress port, the multi-stageswitch fabric is configured to send the plurality of cells associatedwith the packet from the ingress port to the egress port without loss.13. The apparatus of claim 9, wherein: the egress port is a first egressport, a latency associated with a second egress port from the pluralityof egress port being independent from a latency associated with thefirst egress port when the first egress port is congested.
 14. Theapparatus of claim 9, wherein: the egress port is included in a firstsubset of egress ports from the plurality of egress ports, a latencyassociated with each egress port from a second subset of egress portsfrom the plurality of egress ports being independent from a latencyassociated with each egress port from the first subset of egress portswhen each egress port from the first subset of egress ports iscongested, the first subset of egress ports being mutually exclusivefrom the second subset of egress ports.
 15. An apparatus, comprising; aswitch core having a multi-stage switch fabric, the multi-stage switchfabric having a plurality of ingress ports and a plurality of egressports, the plurality of ingress ports numbering at least 1,000 ports,the plurality of egress ports numbering at least 1,000 ports, the switchcore configured to be coupled to a plurality of edge devices via theplurality of ingress ports and the plurality of egress ports, the switchcore configured to receive a packet from an ingress port from theplurality of ingress ports, the switch core configured to send aplurality of cells associated with the packet from the ingress port toan egress port from the plurality of egress ports such that at azero-load latency excluding speed-of-light latency or a congestionlatency excluding speed-of-light latency is less than 15 μsec, and suchthat an edge-device-to-edge-device latency is less than 10 μsec.
 16. Theapparatus of claim 15, wherein the switch core is configured to send theplurality of cells associated with the packet from the ingress port tothe egress port without a store-and-forward delay associated with thezero-load latency for the switch core.
 17. The apparatus of claim 15,wherein: the switch core is configured such that a latency for each cellfrom the plurality of cells is independent of a path within themulti-stage switch fabric of the switch core traversed by that cell whena cabling topology of the switch core is symmetrical and when link ofthe cabling topology are fully operational.
 18. The apparatus of claim15, wherein: the switch core is configured such that the zero-loadlatency excluding speed-of-light latency and the congestion latencyexcluding speed-of-light latency each is independent of a location ofthe ingress port and a location of the egress port, the multi-stageswitch fabric is configured to send the plurality of cells associatedwith the packet from the ingress port to the egress port without loss.19. The apparatus of claim 15, wherein: the egress port is a firstegress port, a latency associated with a second egress port from theplurality of egress port being independent from a latency associatedwith the first egress port when the first egress port is congested. 20.The apparatus of claim 15, wherein: the egress port is included in afirst subset of egress ports from the plurality of egress ports, alatency associated with each egress port from a second subset of egressports from the plurality of egress ports being independent from alatency associated with each egress port from the first subset of egressports when each egress port from the first subset of egress ports iscongested, the first subset of egress ports being mutually exclusivefrom the second subset of egress ports.